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SilenX 14 dBA 400W PSU

May 4, 2003 -- by Mike Chin

Product SilenX 14 dBA 400W PSU
Manufacturer Exotic PC / Fortron-Source
Supplier Exotic PC
MSP US$110

The SilenX 14 dBA power supply was one of the most celebrated products discussed in the forums of Silent PC Review. The posts about the SilenX PSU seemed to begin around February, and quickly became a series of big raves by numerous forum members. The general consensus in the SPCR forums that it is the quietest fan-cooled PSU available. Naturally, the SilenX PSUs quickly got short-listed to be reviewed in SPCR.

ExoticPC sent a sample at the beginning of March. The original intent was to have the review published by around the end of March, but then confusion about the SilenX brand began.

Peter Kim, who was originally employed by ExoticPC, broke away to begin his own independent business under the name of The PSUs sold at are branded SilenX. At the same time, ExoticPC continues to sell SilenX brand PSUs as well.

Without getting into the details, suffice it to say that the SilenX brand PSU supplied by and appear to be essentially identical, notwithstanding changes made by either or since mid-March. Regardless, please note that this review refers specifically to the SilenX 14 dBA 400W PSU sold by ExoticPC. As far as I am aware, ExoticPC have not made any changes in production since then.


The reason Fortron-Source is listed alongside ExoticPC under manufacturer at the top of this page is because they are the OEM supplier. Like several other 300W quiet PSUs reviewed by SPCR, the SilenX 400W is based on a Fortron-Source. On the outside, except for the big ExoticPC SilenX label, this PSU looks identical to a Fortron-Source FSP400-60PFN.

One distinct difference between this PSU and the 300W models by Nexus, Verax and Zalman is that the intake vents are only on the side opposite the fan. The other PSUs mentioned have vents on the "bottom" or cover as well. (See this Nexus example.) Airflow behaves very similar to liquid flow in that it takes the shortest path. Having the intake vents only on the back panel means the air is forced to travel the entire length of the heatsinks in the PSU before it is blown out. This strikes me as better for cooling.

The absence of a manual voltage switch (120/240VAC) indicates that the PSU has Active PFC, which is generally a good thing for electrical efficiency.

The fan visible behind the wire grill is labeled Ahanix, which happens to be the parent company of ExoticPC. The model info is: 825 - 15 - 20; 12V - 0.07A - 0.84W.

The label also identifies Kaimei as the fan maker. It so happens that Kaimei is the original name of a Taiwanese company called Jamicon, who make fans, capacitors and ballast. The closest fan match is JF0825X1E, rated at 19 CFM, 1500 RPM, and 15.9 dBA. This noise rating is the lowest for any fan I've had the opportunity to examine.


These photos of what lies under the hood are revealing.

Quite simply, they are the largest, heaviest heatsinks I've encountered yet in a fan-cooled PSU. I do not have a scale to measure the mass accurately, but it is definitely heavier than the 300W PSUs mentioned above. I thought initially that these heatsinks were installed especially for the SilenX PSU by Fortron-Source, but later discovered that Fortron's own 400W ActivePFC model has the same heatsinks.


  • 14 dB(A) claimed; not clear whether at minumum, typical or maximum power.
  • Output over voltage protection
  • Short circuit protection on all output
  • Reset Table power shut down
  • Approved by:Approved by UL 1950, CSA C22.2 No. 234 Level 3, IEC 950, TUV EN 60950 or VDE 0805, NEMKO EN60950
  • 100% burn-in under high ambient temperature (50C)
  • Vacuum-impregnated transformer
  • MTBF: >50K hours at 25C
  • 100% Hi-pot & ATF tested
  • Line input fuse protection


  • Remote ON/OFF Control
  • Active PFC
  • Temperature range:
    • operating 0C~40C
    • storage -20C~+65C
  • Temperature coefficient: 0.01% / C
  • Transient response: output voltage recovers in less than 1ms max. following a 25% load change
  • Dielectric withstand: input to frame ground 1800 for 1 second
  • Humidity: 5~95% RH
  • Efficiency: 65% at DC24 Input, at full load
  • Power good signal: turn-on delay 100ms to 500ms, off delay 1mS min.
  • Overload protection: 150% max.
  • Inrush current: 60A cold, 80A warm at 264 VAC


AC Input
95~264 VAC, 47~64 Hz
DC Output
Load Regulation
Ripple + Noise
50mV P-P
50mV P-P
120mV P-P
120mV P-P
100mV P-P
50mV P-P
Min Current
Max Current
Max Power
Max Power


There are a total of 7 wire sets:

  • 3 cables, 16" long, each with a single 4-pin IDE drive connector
  • 1 cable, 20" long, with one 4-pin IDE drive connector and one floppy drive power connector
  • 1 cable, 20" long, with two 4-pin IDE drive connectors
  • 20" long cable for main 20-pin ATX connector
  • 20" long cable for dual 12V (P4) connector
  • 3.3V connector on another 20" wire set.

It's noteworthy that 3 of the cables terminate only in one 4-pin connector each. Is that waste or high electrical isolation? Also, none of the cables are very long (generally a good thing for standardard-size PCs), and all are close to the same length.


Parameters Tools
DC load on PSU DBS-2100 PSU load tester
Ambient temperature
Any number of thermometers
Fan / DC voltage regulation
Heath / Zenith SM-2320 multimeter
AC power
Kill-A-Watt Power Meter
Heath AD-1308 Real Time Spectrum Analyzer

The core PSU test tool on SilentPCReview's test bench is the DBS-2100 load tester, made (in Taiwan by D-RAM Computer Company) specifically for testing computer power supplies. The machine consists of a large bank of high power precision resistors along with an extensive selection of switches on the front panel calibrated in Amps (current) and grouped into the 5 voltage lines: +5, +12, -12V, +3.3, -5, +5SR. Leads from the PSU connect into the front panel. It is shown above with leads from a PSU plugged in.

To ensure safe current delivery, the DC output connector closest to the PSU on each set of leads is hooked up to the load tester. This ensures that the current delivered is distributed to as many short leads as possible. When pushing a PSU to its rated output, the heat generated in the wires can be an issue.

The PSU is tested at 5 DC output power levels:

  1. 65W: A very typical DC power draw by many system at low / modest load.
  2. 90W: Established previously as a typical max power draw of a mid-range desktop PC.
  3. 150W: For higher power machines.
  4. 300W
  5. Maximum

Care is taken to ensure that the load on each of the voltage lines does not exceed the ratings for the PSU. The PSU is left running 5~10 minutes at each power level before measurements are recorded.

The DBS-2100 is equipped with 2 individually fused AC outlets and 4 exhaust fans on the back panel. A bypass switch toggles the fans on / off so that noise measurements can be made. The resistors get very hot under high loads.

Kill-A-Watt AC Power Meter is plugged into the AC outlet on the side of the DBS-2100 in the above picture. The AC power draw of the PSU is measured at each of the 4 power loads. The Kill-A-Watt is used to measure:

Efficiency (in AC-to-DC conversion) at each power level. This is the efficiency figure provided by PSU makers. It is obtained by dividing the DC power output (as set on DBS-2100 load) by the AC power consumption. Efficiency varies with load, and also temperature. PSUs seem to run more efficiently when warmer, up to a point. Generally, they are least efficient at low power and most efficient at 40~80% power load. The main advantage of high efficiency is that less power is wasted as heat -- this means a cooler PSU that requires less airflow to maintain safe operating temps (read: quieter.)

Power Factor (PF). This measurement can be read directly off the Kill-A-Watt. In simple terms, it tell us how much AC power is lost to harmonics (unnecessary electromagnetic energy) while driving the PSU. In simple technical terms, it is the difference between the measured V(oltage) x A(mperes) and AC power in Watts. PF varies somewhat depending on load. The ideal PF is 1.0. which means no AC power is lost. A PF of 0.5 means that to deliver 100W in AC to a PSU, your electric company actually uses 200W and and this is often shown in your electric bill as savings (depends on your electric utility company and your account with them). 100W is lost or wasted. Active PF Correction (PFC) power supplies usually have a PF of >0.95. Passive PFC units usually run 0.6 - 0.8. Non-PFC units usually measure 0.5-0.7.

PF is not significant in terms of noise, heat or performance for a PC, but it is relevant to electricity consumption and energy conservation. Here is a simple illustration of worst and best case scenarios based on real tests I conducted on real PSUs (not published): A non-PFC low efficiency PSU vs an Active-PFC high-efficiency PSU.

64% efficiency/ 0.5 PF PSU
78% efficiency / 0.99 PF PSU
DC power delivered
AC power consumed
Lost as heat in AC/DC conversion
Total AC power used*
AC power lost to harmonics
Total power wasted

*Total AC power used: This is what your electric bill would be based on, assuming you drove your PSU to 300W steady DC output, which is unlikely.

As you can see, the differences are remarkable, especially the bottom figures. If you are running large numbers of PCs, there's absolutely no question of the benefits of high PFC and, to a lesser degree, high efficiency.

The Heath / Zenith SM-2320 digital display multimeter, a fairly standard unit, is used to measure the fan voltages and the line voltages of the PSU output. The latter is done via the terminal pin on the front panel, above the connections for the DC outputs from the PSU.

The Test Lab is a spare kitchen measuring 12 by 10 feet, with an 8 foot ceiling and vinyl tile floors. The acoustics are very lively and allows even very soft noises to be heard easily. The PSU under test is placed on a piece of soft foam to prevent transfer of vibrations to the table top. Temperature in the lab is usually ~20C. This is something of a problem as PSUs usually operate in environments that easily reach 45C. Sited next to or above the CPU, the PSU is always subject to external heat. This brings us to the next topic...

In-case Thermal Simulation

The solution is a 100W AC bulb in an empty case with the PSU mounted normally. The distance between the bottom of the PSU and the top of the bulb is about 7 inches. All the case back panel holes are blocked with duct tape. The only significant exit for the hot air in the closed case is the PSU, which is then subject to a fair amount of heat. Still, the bottom front panel case intake hole is very large. In testing, the front of the case is moved so it hangs over the edge of desk, over free air, to ensure good fresh convection airflow. There are no case fans. This is probably a more heat than would be seen by a normal PSU, because in a real case, there are usually other air exits, and at least one case fan.

The simulation means the PSU must cope with the 100W of heat generated by the light bulb plus whatever heat it generates within itself. It is a good simulation when the PSU is actually putting out >100W of DC voltage, although in real-life systems, there would be other air exhausts paths, resulting in a bit lower case temperature. So call it a very demanding test.

Noise Measurements

The Heath AD-1308 is a portable half-octave Real Time Spectrum Analyzer with sound level meter (SLM) functions. Below 40 dBA, its accuracy is poor, limited to 3 dB increments, down to 23 dBA. Some 15 years old, this LED-based unit has long since been displaced by digital devices with better interfaces to PCs. The "A" weighting was used; it most closely approximates the frequency response characteristics of human hearing.

The microphone on the sound meter is positioned within an inch to the side of the PSU fan exhaust to avoid fan turbulence in the microphone itself. The dBA obtained here cannot be compared to any other measurements due to the lack of adherence to a repeatable standard and the uncontrolled reflective environment.

The noise measurements are always accompanied by descriptions of subjective perceptions. Without these, the measurements, which are not that reliable, provide only part of the picture.


Measurements were made at 4 power levels: 65W, 90W, 150W, 300W and 400W. The PSU was allowed to run for 5~10 minutes at each power level before measurements were recorded. The room temperature was 20C.

AC Power
V Fan*
8.5 / 11.7V
38 dBA
41 dBA
41 dBA
41 dBA
41 dBA

VR = Voltage regulation was excellent, ~2% on all lines.

Efficiency, at 66% to 74%, was higher than specified at all power levels beyond the minimum.

*V Fan: The voltage to the fan started at a low 5.3V. At the 65W load, without any external heat to the PSU, the fan voltage ramped up steadily over a 10-15 minute period to 8.5V. When the 100W bulb in the test case was turned on, the fan voltage climbed to over 11.7V within a couple of minutes and simply stayed there at all power levels from 65W to 400W.

**Noise at the default start level was so low that , it was a challenge to hear at all, never mind measure. The measurement cited in the table are basically useless; they are really a laugh, as they don't indicate the real noise of this fan at all. There was also no trace of audible coil whine or buzz from the PSU at any time during testing. This is quite a feat considering how quiet the fan sometimes runs. However, the noise did not stay at the startup level.

  • At the startup voltage, you have to strain to hear it at 6 inches distance in a super quiet room.
  • At the low load of 65W, the fan reaches 8.5V. It is definitely noisier than at startup, but is inaudible more than 1~2 feet away in most environments.
  • At 12V, the fan is clearly audible beyond 3 feet, but still quieter than a Panaflo "L" at 12V. The fan manufacturer claims 16 dBA @ 1 meter at 12V. In a brief visit to the UBC anechoic chamber, I measured ~18 dBA at 1 meter.
  • The overall characteristic of this fan is smooth and clean. At 12V, the fan blades make a slight whining noise. At any voltage under 9-10V, the fan simply ramps down smoothly with virtually NO electronic noise, clicking, buzzing or any other typical extraneous noises that most DC fan produce when undervolted. It is actually cleaner sounding than the Panaflo L. However, its airflow is significantly less. The manufacturer specifies 19 CFM.

TEMPERATURES were measured for this PSU because the airflow seemed so low and the internal temperature felt like it was climbing high. This is a departure from recent PSU reviews, for which temperature testing was not done. Given the low airflow of the fan and the high power capacity of the fan, I felt this was necessary for a full understanding of this product. The thermal sensor was inserted into the hottest point in the fan outflow as shown below.

The testing done in this section is somewhat complex, so you may want to pay close attention.

Temp A (°C) w/100W light

3 min shutoff
Temp B (°C) w/o light
Temp C (°C) w/ light + Panaflo
28C / 6V
29C / 7V
32C / 8V
41C / 8V

1 min shutoff
  • Temp A numbers show the outflow air temperature at the various power levels with the 100W bulb turned on and the case sealed except for the PSU exhaust. The PSU was kept powered up from startup to 400W power level, a period of over 30 minutes. After about 3 minutes at 400W, when the air outflow temp looked to increase past 57C, the PSU turned itself off.

    One could actually anticipate the shutdown: The total AC power drawn by the PSU began with a high of around 570W, but then over the next couple of minutes, steadily dropped to under 540W, at which point the power-off occurred without any drama. Resetting the PSU (not with the load at full!!) restored power immediately. It is some kind of current clamp mechanism; it may be set a bit too low on this one? It is difficult to judge.

    Because I was concerned that the remaining heat in the PSU might damage it with the fan turned off, I set the PSU load tester for minimal voltage, pulled the 100W AC light bulb, removed the cover of the case, and turned the PSU turned back on. The SilenX turned back on without a hitch. It took a little under 10 minutes of low power operation for the air outflow temperature to stabilize around 32C.

  • Temp B numbers show the airflow air temperature with the PSU in the case without any light bulb, and with the case side cover removed. The PSU only had to keep itself cool.
  • Temp C numbers show the airflow air temperature under the same conditions as Temp A (with 100W light bulb on 7" below PSU, case closed) with one addition: a Panaflo "L" 80mm on the back case panel. The second number in the data columns for Temp C refers to the voltage fed to that Panaflo.

Why the additional fan?

  • This additional case fan does not add any more noise than already emitted by the SilenX under normal conditions.
  • Almost every system has at least one case airflow fan, so this is a realistic real-use application.
  • The case fan voltage was deliberately selected to provide the greatest amount of airflow while remaining more-or-less masked by the PSU fan.

As the temperature results for 65, 150 and 300 watt output levels show, the addition of that Panaflo L case fan made a dramatic difference in the temperature of the PSU exhaust. This is precisely what was expected. The PSU fan rose to ~10V after 5~10 minutes at 65W, and climbed to 12V at 150W and beyond. However, exhaust temperature stayed very modest even at 300W output for 5~10 minutes.

The shutdown again at 400W with the case fan blowing was somewhat unexpected. Admittedly, the PSU had not actually been turned off between Temp B tests and the Temp C tests. I suspect that one or more key components in the PSU were still at elevated temperatures, which might caused the protection to trigger early. Neither of the auto-shutdowns experienced during testing seems to have caused any kind of damage to the PSU. (It continues to work away on a SPCR folding @ home system today.)

A final comment: Full power testing of PSUs for any length of time is a very demanding test, generally tougher than what real use conditions can demand. SPCR's bench testing is steady-state and can be extended indefinitely until the PSU burns; in real world applications, PSUs in PCs rarely get anywhere close to this kind of abuse (except maybe in a serious server room, which is a different application altogether).


The SilenX 14 dBA advances the state of quiet fan-cooled power supplies by another few decibels. On turn-on, the PSU is so quiet as to be virtually inaudible by everyone who tried to hear it while it was in the test lab. Its noise level doesn't stay at that super low level, however. At the 8.5V PSU fan level at which the SilenX fan seems to stabilize, the noise level is very low, a bit lower than any other PSUs thus far. (I am sure some of you are beginning to groan at that phrase; unfortunately, it fits. The last ones were the quietest, but now this one is even quieter! What to say?)

The difference is audible in a real system, inside a real PC -- if the rest of your components are quiet enough. There seems little doubt that a case fan is a real necessity with the low-airflow SilenX unless you are building a low power dissipation system with super-low impedance to airflow. A case fan is par for even the silent course anyway...

The strengths of the SilenX lies in:

  • heavy build quality, with massive heatsinks
  • excellent thermal protection,
  • good directed airflow design,
  • good quality active PFC with universal voltage input
  • vanishingly low noise

The trick is to understand how best to use it in the context of its:

  • minimal cooling airflow

You have to keep additional hot air from other case components from getting into the PSU in order that its fan remain spinning as slowly as possible. The SilenX is a classic case of a product optimized for one thing strongly enough to be imbalanced. It goes to the nth degree in pursuit of silence without actually losing the fan altogether. As a tool for silent-savvy builders and enthusiasts, the SilenX 14 dBA 400W PSU is recommended with caution about its low airflow fan. Use it without full understanding, and the heat & noise level may disappoint. Use it carefully, and the PSU will help you make a quieter PC.

Our thanks to ExoticPC for the SilenX review sample and their kind support.

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