Nexus NX-4090 "Real Silent" PSU

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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 to 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 new 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 21°C and 18 dBA, with input of 121 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.


1. VOLTAGE REGULATION was very good, within -/+2% on all lines in any combination of loads. The low and high voltage seen on each of the main lines is shown:

  • +12V: 12.30 to 12.45
  • +5V: 4.90 to 5.08
  • +3.3V: 3.29 to 3.40

2. EFFICIENCY was very good throughout the power load range, starting high and staying high. The efficiency / power output ratio is a pretty flat curve except at maximum power, where it dropped off a bit. 76~78% efficiency in the range that really counts (under 200W where 99% of computers run most of the time) is not quite in the top league (which is >80% these days), but it is very good and much better than the NX3500, There's no question of progress here.

3. POWER FACTOR was typical for passive power factor correction unit, ranging from 0.62 at low loads to a high of 0.69 at maximum power load.

4. FAN VOLTAGE & NOISE: The test environment is live, so readings are higher than would be obtained in an anechoic chamber readings. The fan receives full voltage (10-11V) for a couple of seconds upon startup to ensure that it always starts. The default voltage just after a cool start was ~3.7V but climbed quickly to 4.1V.

Subjectively, the Nexus NX4090 is very quiet. After the startup burst, the 120mm fan has virtually no bearing noise. This is the same characteristic noted in the NX3500. Even at 7V, the primary noise is the relatively benign whooshing sound of air turbulence. No bearing chatter, whistling or whining.

The measured noise at startup was about as low as the quietest PSU tested. However, the fan sped slightly under load -- 3.7V at start and 4.0~4.1V under 65W load. The noise level of 21 dBA/1m is a touch higher than the Seasonic Super Tornado (Rev.A3) we tested, which stayed at 18 dBA/1m to over 100W load and rose to 21 dBA/1m only at 150W.

The first significant change came at the 150W output level where the fan voltage reached 4.4V and the noise went up slightly to a still very quiet 24 dBA/1m. There was a more significant rise to 200W where noise measured 30 dBA/1m. From 200W to 250W, the voltage to the fan climbed to the maximum the internal voltage controller is capable of delivering. It stayed at 11.25V and 38 dBA/1m from 250W all the way to full power.


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

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

Ultra X-Connect @ 65W (33 dBA/1m)

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


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.

Comparing the NX4090 to the Seasonic Tornado 400 should give a good frame of reference. 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 Nexus NX4090 is a significant improvement on an already good quiet PSU. Efficiency is much better than the earlier NX3500, and its increased power capacity and ATX12V v2.0 compatibility are welcome. Its distinctive orange colored fan remains the smoothest, least obtrusive 120mm fan I've heard in a PSU. The Nexus NX4090's fan noise characteristic puts it among the quietest of power supplies we've tested.

We could not confirm the 16.2 dBA claim by Nexus. The noise floor of our test room is above that level. It would seem that the only time such a low volume could be reached is immediately after turn on without a load and in moderate room ambient temperature.

Aside from the added power and features already mentioned, the main advantage of the NX4090 over the NX3500 is that it remains at a quieter level to a high power output. This was confirm in a quick A/B comparison between samples of the two models on hand. The fan controller in the NX4090 has a more modest rising voltage / temperature curve. Perhaps the designers have taken advantage of the extra efficiency which means cooler operation to reduce the fan speed a bit. Between 100W to 200W loads, it is anywhere between 2 to 5 dBA/1m quieter than its predecessor. This is a very audible and real improvement, as it happens to be where the vast majority of current PC system DC power load lies in actual use.

As with other 120mm fan PSUs, in a case with minimal airflow restrictions, it may be possible to run a midrange power system without any other case fans due to the large air-moving capability of the big fan. Note that with all setups that rely on the PSU to exhaust much of the heat, with hot components, there is always the risk of the temperature in the PSU under load, with the fan speeding up and getting noisier as a result.

The Nexus NX4090 has no obvious weaknesses and many strengths:

  • Very smooth, quiet fan
  • Pretty high efficiency
  • Good stability and voltage regulation
  • Good self-cooling
  • Good directed airflow design

It certainly deserves our recommendation.

Our thanks to our sponsor EndPCNoise for the Nexus NX3500 review sample and for their continued support.

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