Cooler Master G550M 550 W Review 5

Cooler Master G550M 550 W Review

Ripple Measurements »

Advanced Transient Response Tests

We monitor the response of the PSU in two different scenarios in these tests. First, a transient load (10 A at +12V, 5 A at 5V, 5 A at 3.3V, and 0.5 A at 5VSB) is applied to the PSU for 200 ms while the latter is working at 20% load. In the second scenario, the PSU, while working at 50% load, is hit by the same transient load. In both tests, we measure the voltage drops the transient load causes using our oscilloscope. The voltages should remain within the regulation limits defined by the ATX specification. We must stress here that the above tests are crucial since they simulate transient loads a PSU is very likely to handle (e.g., booting a RAID array, an instant 100% load of CPU/VGAs, etc.). We call these tests "Advanced Transient Response Tests", and they are designed to be very tough to master, especially for PSUs with capacities below 500 W.


Advanced Transient Response 20%
VoltageBeforeAfterChangePass/Fail
12 V12.058V11.824V1.94%Pass
5 V5.050V4.984V1.31%Pass
3.3 V3.384V3.289V2.81%Pass
5VSB5.051V5.007V0.87%Pass



Advanced Transient Response 50%
VoltageBeforeAfterChangePass/Fail
12 V12.014V11.787V1.89%Pass
5 V5.007V4.938V1.38%Pass
3.3 V3.343V3.244V2.96%Pass
5VSB5.007V4.966V0.82%Pass


Voltage drops in both tests were controlled well on all rails, despite the low overall capacity of the G550M, which is a huge handicap here. We would ideally like to see deviations closer to 1% on the +12V rail; however, we cant be very picky since this is a low-capacity PSU of the budget category.


Below, you will find the oscilloscope screenshots we took during Advanced Transient Response Testing.

Transient Response at 20% Load



Transient Response at 50% Load



Turn-On Transient Tests

We measure the response of the PSU in simpler scenarios of transient loads—during the power-on phase of the PSU—in the next set of tests. In the first test, we turn the PSU off, dial the maximum current the 5VSB can output, and then switch on the PSU. In the second test, we dial the maximum load +12V can handle and start the PSU while the PSU is in standby mode. In the last test, while the PSU is completely switched off (we cut off power or switch off the PSU's on/off switch), we dial the maximum load the +12V rail can handle before switching the PSU on from the loader and restoring power. The ATX specification states that recorded spikes on all rails should not exceed 10% of their nominal values (e.g., +10% for 12V is 13.2V and 5.5V for 5V).


We measured a small spike on the 5VSB rail, which, however, is much lower than the limit. The slope wasn't as smooth as we would like in the other two tests, but voltage overshoots in the last two tests were far below the corresponding limit, so none of those will endanger the system. To wrap up, I think there is some room for improvement here.
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Dec 25th, 2024 09:37 EST change timezone

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