Bitfenix Whisper Series 550W PSU Review

Transient Response Tests

Advanced Transient Response Tests

For details on our transient response testing, please click here.

Ιn these tests, we monitor the BWG550M's response in two different scenarios. First, a transient load (10A at +12V, 5A at 5V, 5A at 3.3V, and 0.5A at 5VSB) is applied for 200ms while the PSU works at 20 percent load. In the second scenario, Bitfenix's contender is hit by the same transient load while operating at 50 percent load. In both tests, we use our oscilloscope to measure the voltage drops caused by the transient load. The voltages should remain within the ATX specification's regulation limits.

These tests are crucial because they simulate the transient loads a PSU is likely to handle (such as booting a RAID array or an instant 100 percent load of CPU/GPUs). We call these tests "Advanced Transient Response Tests," and they are designed to be very tough to master, especially for a PSU with a capacity of less than 500W.

Advanced Transient Response at 20 Percent

VoltageBeforeAfterChangePass/Fail
12V12.043V11.909V1.11%Pass
5V5.052V4.994V1.15%Pass
3.3V3.334V3.263V2.13%Pass
5VSB5.064V5.014V0.99%Pass

Advanced Transient Response at 50 Percent

VoltageBeforeAfterChangePass/Fail
12V12.010V11.910V0.83%Pass
5V5.037V4.976V1.21%Pass
3.3V3.320V3.253V2.02%Pass
5VSB5.048V4.995V1.05%Pass

The +12V rail's transient response is pretty good, given the unit's low capacity. Deviations are very low on the other rails, and the 3.3V rail registers high performance. We haven't seen such low deviation on this rail for quite a while.

Here are the oscilloscope screenshots we took during Advanced Transient Response Testing:

Transient Response At 20 Percent Load

Transient Response At 50 Percent Load

Turn-On Transient Tests

In the next set of tests, we measured the response of the PSU in simpler transient load scenarios—during its power-on phase.

For the first measurement, we turned off the BWG550M, dialed in the maximum current its 5VSB rail could output, and switched the PSU back on. In the second test, we dialed the maximum load the +12V rail could handle and started the 550W supply while it was in standby mode. In the last test, while the PSU was completely switched off, we dialed the maximum load the +12V rail could handle before switching it back on from the loader and restoring power. The ATX specification states that recorded spikes on all rails should not exceed 10 percent of their nominal values (+10 percent for 12V is 13.2V, and 5.5V for 5V).

The only spike we noticed appeared during the last test, and it was too small to pose a threat.

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6 comments
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  • turkey3_scratch
    Bitfenix did the right thing pairing with CWT here. This is a great unit!
  • Aris_Mp
    Indeed, its performance was a nice surprise for me as well. It's good to see some new competition in this market.
  • Nuckles_56
    Damn, I wonder what Australian pricing will be like for this unit, as I'd be almost tempted to replace my current PSU with a quieter one like this if it is priced well
  • MarekRMac
    Hi, please give me quick advice: Bitfenix Whisper M 550W or Corsair RM550x ?
  • Aris_Mp
    2391142 said:
    Hi, please give me quick advice: Bitfenix Whisper M 550W or Corsair RM550x ?


    Which ever you can find at a lower price. Performance wise they are very close.
  • jonnyguru
    One noticeable difference between the RMx and the Whisper is that the RMx uses an MCU for the fan controller instead of the standard thermistor/transistor circuit in the BitFenix product.