Clever Power SPS-400

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Ambient conditions during testing were 21°C and 20 dBA, with input of 120 VAC / 60 Hz measured at the AC outlet.

Clever Power SPS-400 TEST RESULTS
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.


Any new or unusual way of doing things always has some element of risk. The test bench will determine whether the fancy airflow and blower fan actually have any practical benefit for quiet computing.

1. VOLTAGE REGULATION was excellent, within ¬Ī2% on all lines at every load. The 12V was consistently low, but only by 0.1~0.2 V.

  • +12V: 11.8 to 11.9
  • +5V: 4.9 to 5.0
  • +3.3V: 3.3

2. EFFICIENCY was fairly average by today's standards, staying in the 78-80% range for the crucial 150-250W range. When this PSU was released a year ago these numbers would have been excellent, but the competition in this area has stiffened a lot in the past year.

3. POWER FACTOR was quite good, ranging between 0.65 and 0.73. While it's obviously not an active PFC unit, we've seen much worse numbers from more expensive power supplies.

4. FAN, FAN CONTROLLER and NOISE: The Clever Power starts up with a quick 12V burst to make sure the fan starts and immediately drops to the lowest voltage required to keep it spinning, around 4.3V. At this voltage, the fan is practically inaudible from 1 meter. The noise it produced was close to our ambient noise level of ~20 dBA. Could it be that Clever Power's claim of 18-25 dB be accurate?

Of course, if you've been reading carefully, you will have noticed that our voltage table starts at 6.4V. Why not 4.3V? The 4.3V reading that we measured was obtained in open air while the PSU was cold. Installing the Clever Power in our test setup had the immediate effect of boosting the fan voltage (and noise). The noise level of 31 dBA/1m at 65W would not be acceptable in a quiet computer; if the PSU is mounted in an actual case, the bass hum of the fan will never totally disappear.

Moving to a higher load has an immediate and audible effect on the Clever Power. The transitions between voltages are not very smooth, and changes in fan speed are clearly audible. The thermal sensor is sensitive enough that it responds audibly when the exhaust path is blocked.

The fan controller appears to be very conservatively tuned, and responds linearly to increases in load / heat. Almost all of the adjustment range is used below 150W, which means that in a high powered system, the PSU fan may never run below ~9V. This is too high a voltage to produce acceptable noise levels. The designers of this PSU would do well to examine the more "stepped" or exponential fan speed-to-heat response curves of the best quiet PSU fan controllers.

MP3 Sound Recordings of Clever Power SPS-400

Clever Power SPS-400 @ 65W (31 dBA/1m)

Clever Power SPS-400 @ 90W (33 dBA/1m)

Clever Power SPS-400 @ 150W (37 dBA/1m)

Sound Recordings of Comparative Power Supplies

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

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

Seasonic Tornado 400 @ 200W (24 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.

To set the volume to a realistic level (similar to the original), try playing the Nexus 92 fan reference recording above 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.


There was a considerable amount of thought put into designing the Clever Power SPS-400. A negative pressure airflow system and a built-in power strip are not common features for a power supplies. Unfortunately, it seems that not enough time was spent on the test bench; tampering with the internal airflow does not seem to have produced any tangible benefits. It is true that the AC outlets are indirectly made possible by the use of a blower-style fan that does not require the whole back to be used as an exhaust vent. However, the fan controller that the blower is paired with makes it difficult to consider this power supply for use in even a moderately quiet system. A system with a fresh air intake duct for the PSU might prevent the blower fan from ramping up in speed.

The extra AC outlets could be quite useful depending on how your system is set up. For people who want to centralize their cable management (and don't mind adding even more cables to the tangle behind their case), this could be quite a welcome addition. The 2A maximum current may be too low for some applications though. In North America, larger CRT monitors and laser printers routinely draw more than 2A. For countries that have 240V power systems this will be less of an issue because the higher line voltage effectively halves the current draw of all electrical appliances.

For $45, the Clever Power is cheap enough that it might be worth integrating it into a system that is specially designed for it. We had no issues about either its stability or its efficiency. However, anyone looking for a cheap quiet power supply to drop into their existing system would be best advised to look elsewhere. Just about any PSU in our Recommended table will be quieter. This power supply will be a significant source of noise in any situation in which it is expected to exhaust warmed air from a case.

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Much thanks to Clever Power for the opportunity to examine this power supply.

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