Fortron-Source Power Blue Storm AX500-A PSU

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For a fuller understanding of ATX power supplies, please read our article Power Supply Fundamentals & Recommended Units. Those who seek source materials can find Intel's various PSU design guides, closely followed by PSU manufacturers, at Form Factors.

For a complete rundown of testing equipment and procedures, please refer to the article SPCR's Revised PSU Testing System. It is a close simulation of a moderate airflow mid-tower PC optimized for low noise.

In the test rig, the ambient temperature of the PSU varies proportionately with its actual output load, which is exactly the way it is in a real PC environment. But there is the added benefit of a precise high power load tester which allows incremental load testing all the way to full power for any non-industrial PC power supply. Both fan noise and voltage are measured at various loads. It is, in general, a very demanding test, as the operating ambient temperature of the PSU often reaches 40°C or more at full power. This is impossible to achieve with an open test bench setup.

Great effort has been made to devise as realistic an operating environment for the PSU as possible, but the thermal and noise results obtained here still cannot be considered absolute. There are far too many variables in PCs and far too many possible combinations of components for any single test environment to provide infallible results. And there is always the bugaboo of sample variance. These results are akin to a resume, a few detailed photographs, and some short sound bites of someone you've never met. You'll probably get a reasonably good overall impression of that person, but it is not quite the same as an extended meeting in person.

SPCR's high fidelity sound recording system was used to create MP3 sound files of this PSU. As with the setup for recording fans, the position of the mic was 3" from the exhaust vent at a 45° angle, outside the airflow turbulence area. The photo below shows the setup. All other noise sources in the room were turned off while making the sound recordings.

Ambient conditions during testing were 20°C and 20 dBA, with input of 120 VAC / 60 Hz measured at the AC outlet.

DC Output (W)
AC Input (W)
Intake Temp (°C)
PSU Exhaust (°C)
Fan Voltage
Noise (dBA/1m)
Power Factor

NOTE: The ambient room temperature during testing varies a few degrees from review to review. Please take this into account when comparing PSU test data.


As mentioned above, despite the "500" in the model number and the 500W marketing blurb on the retail box, the Blue Storm is rated up to 460W. Because of the discrepancy between these two numbers we feel that the 460W rating may be more conservative (and truthful) than the ratings specified by many other companies. This speculation is borne out by the fact that efficiency began to rapidly decline at around the 460W mark. Many other power supplies exhibit this rapid decline before their rated spec, indicating that they are operating beyond their capabilities.

1. VOLTAGE REGULATION was good, ±4% or better on all lines at any of the test loads. The ATX 2.2 standard specifies voltage regulation of ±5% on a positive lines, so ±4% is a reasonable margin of error

  • +12V: 12.11 to 12.45
  • +5V: 4.78 to 4.91
  • +3.3V: 3.19 to 3.30

2. EFFICIENCY was just short of top notch. The highest efficiency power supply that we tested peaked at 88%. However, its efficiency peaks at 300W, and at 90W, the efficiency is a much lower 76%. By comparison, the Blue Storm has an extremely flat efficiency curve, and its peak efficiency is between 150W and 250W: right in the typical power range. There are other power supplies that have a higher peak efficiency, but these units typically reach this peak at wattages that are beyond what most systems draw. Furthermore, the difference between the highest and the lowest measured efficiency for the whole 460W range was just 3%. Our measurements place the Blue Storm well above its rated efficiency of >70%, and it is 10-17% more efficient than the last Fortron PSU we tested, the FSP350-60PN "Aurora".

3. POWER OUTPUT: The Blue Storm had no trouble meeting its specified maximum of 460W. It even ran for about 20 minutes at almost double its 160W maximum rating for the +3.3V/+5V combination before we realized that we had overloaded it. The wattage ratings of this power supply may be more conservative than most, and this is a good thing.

NOTE on PCI-E CURRENT CAPACITY: There was some question about the maximum output capacity for PCI-Express because of the recent changes in the spec by Intel and nVidia. So to avoid confusion, a quick call was placed to Fortron. They confirmed that up to 75W was available on for PCI-e. The latest spec demands as much as 150W. As far as we know, PCI-e VGA cards that demand that much power are not on the market yet, but you should be aware that 75W is the recommended maximum on this PSU.

4. POWER FACTOR: There is no mention of power factor in any of the Blue Storm's marketing material or its specification sheets. However, its power factor is in line with other units with passive power factor correction, which ranges between 0.63 and 0.67.

5. FAN & FAN CONTROLLER: The Blue Storm is unusual for a Fortron power supply because its fan is manufactured by Protechnic rather than Yate Loon. While the Protechnic is not the quietest fan we have heard, it is quite smooth, and because it is a sleeve-bearing, it does not exhibit the clicking so common in ball-bearing fans. A lower airflow version of this fan would have been a better choice from an acoustics point of view, but given how "soon" the fan controller brings it up to 12V, this may not have been viable from a cooling standpoint.

The fan controller is quite responsive. Changes in temperature are quickly mirrored by changes in fan voltage. The rate of change is close to the threshold of perception. Listening closely, it is possible to hear the fan slowly increasing in speed. However, it is unlikely that the changes in fan voltage are sudden enough to be noticeable as background noise. Unless one is specifically listening for the change in fan speed it is unlikely to be noticed.

There are two concerns that we had with the fan controller on the Blue Storm:

  • One is the start voltage. The low floor for the fan voltage seems to be around 5.3 volts. Many competitive quiet PSUs start below 5V. In a system that is otherwise quiet, this difference is audible with the typical mid-to-low speed 12V fan employed in quiet PSUs.
  • The other concern is that it increases in voltage too soon. The fan voltage begins to increase at about 150W output, and by 200W output the fan voltage is 7.8V and it produces 36 dBA at one meter: No longer quiet. This is an active power range where changes in fan speed are likely to be audible. While this may be good design from a cooling standpoint, it is not such a good design from a low noise point of view.

6. NOISE: The noise of the Protechnic fan starts out mostly as airflow. There is a small amount of low frequency motor hum that is noticeable in an otherwise silent room, but it is fairly constant and inoffensive. As fan voltage increases, the hum becomes more evident and increases in pitch, bringing the noise further into the range of frequencies to which humans are most sensitive.

In a case, the starting noise level (and, most likely, the idle level) is pretty low, and probably good enough for most users. You may not want to sleep next to it, but during daylight hours the ambient noise would probably be loud enough to cover it. At higher loads, the hum of the motor could easily become irritating as a background drone. It is the volume of the noise that is the problem, not the character, so using this power supply in a low power system might be viable. But, then again, why use a 460W power supply in a low power system?

MP3 Sound Recordings of FSP Blue Storm AX500-A

FSP Blue Storm AX500-A @ <100W (26 dBA/1m)

FSP Blue Storm AX500-A @ 150W (29 dBA/1m)

FSP Blue Storm AX500-A @ 200W (36 dBA/1m)

There was no need to make recordings at higher power levels; it's simply too loud.

Sound Recordings of Comparatives

Seasonic Tornado 400 @ 65W (19 dBA/1m)

Nexus NX4090 at @150W (24 dBA/1m)

Seasonic Tornado 400 @ 200W (24 dBA/1m)

Reference: Nexus 92mm case fan @ 5V (17 dBA/1m)


These recordings were made with a high resolution studio quality digital recording system. The microphone was 3" from the edge of the fan frame at a 45° angle, facing the intake side of the fan to avoid direct wind noise. The ambient noise during all recordings was 18 dBA or lower.

To set the volume to a realistic level (similar to the original), try playing the Nexus 92 fan reference recording and setting the volume so that it is barely audible. Then don't reset the volume and play the other sound files. Of course, tone controls or other effects should all be turned off or set to neutral. For full details on how to calibrate your sound system to get the most valid listening comparison, please see the yellow text box entitled Listen to the Fans on page four of the article SPCR's Test / Sound Lab: A Short Tour.


The Fortron Source Power Blue Storm AX500-A is a great improvement over the last Fortron PSU that we reviewed. Efficiency is definitely this power supply's greatest strength. Noise levels between the Blue Storm and the FSP350-60PN Aurora measured within two dBA, but the Blue Storm is quieter subjectively.

In a wider comparison with power supplies from other acoustics-focused manufacturers, the Blue Storm fares less well. There are units with quieter fans and fan controllers that output less voltage to a higher power output level, although few of them will beat the Blue Storm in efficiency. Kudos to Fortron for using a sleeve-bearing fan instead of a ball-bearing model, which would have been noiser. Still, this sleeve bearing fan was not really quiet enough to push the Blue Storm into the top ranks of quiet PSUs.

The retail pricing seems quite attractive for its power rating, but this is such a variable that it is difficult to comment on with confidence. The inclusion of Molex connectors with grips is also a point in the Blue Storm's favour. We look forward to seeing this feature on more power supplies from Fortron, and hope that such connectors become industry standard.

Overall, the Blue Storm is a well-rounded power supply that suits many applications. Its flat efficiency curve makes it suitable for use in both high and low power applications. Although the noise it produces at higher output levels would be unacceptable to a hardcore silencing enthusiast, it is likely that in a high powered system there would be other, greater sources of noise.

* * *

Much thanks to Fortron Source for the opportunity to examine the Power Blue Storm AX500-A.

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