SilenX 14 dBA 400W PSU

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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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