FSP Hydro PTM 650W PSU Review: Clean, Quiet Power for Mid-Range PCs

Transient Response Tests

Advanced Transient Response Tests

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

Ιn these tests, we monitor the HPT650M's response in several scenarios. First, a transient load (10A at +12V, 5A at 5V, 5A at 3.3V, and 0.5A at 5VSB) is applied for 200ms as the PSU works at 20 percent load. In the second scenario, it's hit by the same transient load while operating at 50 percent load.

In the next sets of tests, we increase the transient load on the major rails with a new configuration: 15A at +12V, 6A at 5V, 6A at 3.3V, and 0.5A at 5VSB. We also increase the load-changing repetition rate from 5 Hz (200ms) to 50 Hz (20ms). Again, this runs with the PSU operating at 20 and 50 percent load.

The last tests are even tougher. Although we keep the same loads, the load-changing repetition rate rises to 1 kHz (1ms).

In all of the tests, we use an 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 "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.  

We should note that the ATX spec requires for capacitive loading during the transient rests, but in our methodology we chose to apply the worst case scenario with no extra capacitance on the rails. 

Advanced Transient Response at 20 Percent – 200ms

VoltageBeforeAfterChangePass/Fail
12V12.112V11.975V1.13%Pass
5V5.080V4.943V2.70%Pass
3.3V3.356V3.194V4.83%Pass
5VSB5.068V5.016V1.03%Pass

Advanced Transient Response at 20 Percent – 20ms

VoltageBeforeAfterChangePass/Fail
12V12.120V11.925V1.61%Pass
5V5.080V4.912V3.31%Pass
3.3V3.356V3.192V4.89%Pass
5VSB5.073V5.018V1.08%Pass

Advanced Transient Response at 20 Percent – 1ms

VoltageBeforeAfterChangePass/Fail
12V12.124V12.000V1.02%Pass
5V5.080V4.917V3.21%Pass
3.3V3.355V3.159V5.84%Pass
5VSB5.077V5.021V1.10%Pass

Advanced Transient Response at 50 Percent – 200ms

VoltageBeforeAfterChangePass/Fail
12V12.088V11.982V0.88%Pass
5V5.053V4.906V2.91%Pass
3.3V3.329V3.161V5.05%Pass
5VSB5.029V4.978V1.01%Pass

Advanced Transient Response at 50 Percent – 20ms

VoltageBeforeAfterChangePass/Fail
12V12.094V11.945V1.23%Pass
5V5.054V4.892V3.21%Pass
3.3V3.328V3.145V5.50%Pass
5VSB5.033V4.999V0.68%Pass

Advanced Transient Response at 50 Percent – 1ms

VoltageBeforeAfterChangePass/Fail
12V12.096V11.980V0.96%Pass
5V5.054V4.889V3.26%Pass
3.3V3.328V3.127V6.04%Fail
5VSB5.034V4.977V1.13%Pass

The +12V rail's result lands close to 1%, which reflects decent performance. It would, however, be better to see the HPT650M closer to its competition.

Voltage drops are notable on the minor rails, causing FSP's HPT650M to land in last place on our charts. The 3.3V rail's voltage falls way below 3.2V. In one of the tests, it even fails to stay within the ATX specification's tolerance.

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

Transient Response At 20 Percent Load – 200ms

Transient Response At 20 Percent Load – 20ms

Transient Response At 20 Percent Load – 1ms

Transient Response At 50 Percent Load – 200ms

Transient Response At 50 Percent Load – 20ms

Transient Response At 50 Percent Load – 1ms

Turn-On Transient Tests

In the next set of tests, we measure the HPT650M’s response in simpler transient load scenarios—during its power-on phase.

For our first measurement, we turn the power supply off, dial in the maximum current the 5VSB rail can handle, and switch the PSU back on. In the second test, we set the +12V rail's maximum load and start the PSU while it is in standby mode. In the last test, with the PSU switched completely off, we dial in the +12V rail's maximum load before 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 5VSB slope is perfect. Our results in the other two tests are satisfactory as well.

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  • AnimeMania
    Is there a reason why they put the word "Hydro" in the title?
  • SR-71 Blackbird
    Thanks Aris , nice review , much appreciated.
  • average joe
    they want to market it as water cooler compatible... yeah i know..
  • average joe
    there used to be some really crappy power supplies in the world but now most of them are fine. you had to be really careful or you burn up everything. that doesn't happen anymore.
  • average joe
    there really only three companies that make PSU now and they all just badged for different brands. one might insist on using higher grade but its still a superflower.
  • average joe
    rosewill capstones are usually superflower and 1/2 the money
  • police_leduc113
    Even so, for guys like me who only use a "normal pc" without OC, this one will do just fine right? Cause i got it from black friday for the right price, while Seasonic stuff are insanely expensive in my country
  • SR-71 Blackbird
    Some of the Rosewill Capstones , don't get good reviews from buyers , I avoid them.
  • Co BIY
    POLICE_LEDUC113 - Yes, This is a better than average power supply. Not the absolute best but priced in the US with the absolute best. If you got it at good price compared to the competition then it will do well for you.