Test Setup

All measurements were performed using two Chroma 6314A mainframes equipped with the following electronic loads: six 63123A [350 W each], one 63102A [100 W x2], and one 63101A [200 W]. The aforementioned equipment is able to deliver 2500 W of load, and all loads are controlled by a custom-made software. We also used a Picoscope 3424 oscilloscope, a Picotech TC-08 thermocouple data logger, a Fluke 175 multimeter, and an Instek GPM-8212 power meter. We also included a wooden box, which, along with some heating elements, was used as a hot box. Finally, we had at our disposal four more oscilloscopes (Rigol 1052E and VS5042, Stingray DS1M12, a second Picoscope 3424), and a CEM DT-8852 sound level meter. In this article, you will find more details about our equipment and the review methodology we follow. Finally, we conduct all of our tests at 40 - 45°C ambient in order to simulate with higher accuracy the environment seen inside a typical system; the 40 - 45°C being derived from a standard ambient assumption of 23°C and 17 - 22°C being added for the typical temperature rise within a system.

Voltage Regulation

The following charts show the voltage values of the main rails, recorded over a range of 60 W to the maximum specified load, and the deviation (in percent) for that same load range.

5VSB Regulation

The following chart shows how the 5VSB rail deals with the load we throw at it.

Hold-up Time

The hold-up time is a very important characteristic of a PSU and represents the amount of time, usually measured in milliseconds, that a PSU can maintain output regulations as defined by ATX spec, despite a loss of input power. It is, in other words, the amount of time that the system can continue to run without shutting down or rebooting during a power interruption. At maximum continuous output load, the ATX spec sets the minimum hold-up time to 16 ms. In the following screenshot, the blue line is the mains signal while the yellow line is the "Power Good" signal. The latter is de-asserted to a low state when any of the +12V, 5V or 3.3V output voltages fall below the undervoltage threshold or after the mains power has been removed for a sufficiently long time to guarantee that the PSU cannot operate anymore. In this case, the G-550 failed to reach the minimum hold-up time of 16 ms.

Inrush Current

Inrush current or switch-on surge refers to the maximum, instantaneous input-current drawn by an electrical device right as it is turned on. PSUs produce large inrush current right as they are turned on because of the charging current of the APFC capacitor(s). Large inrush current can cause the tripping of circuit breakers and fuses and may also damage switches or relays. The lower the inrush current of a PSU turn-on, the better.

Voltage Regulation and Efficiency Measurements

The first set of tests revealed the stability of the voltage rails and the efficiency of the G-550. The applied load was equal to (approximately) 20%, 40%, 50%, 60%, 80%, 100% and 110% of the maximum load that the PSU can handle. In addition, we conducted two more tests. In the first test, we stressed the two minor rails (5V and 3.3V) with a high load while the load at +12V was only 2 A, and, in the second test, we dialed the maximum load that the +12V rail could handle while the load on the minor rails was minimal.


The PSU registered high overall efficiency, fully justifies its Gold rating. Also, voltage (or load) regulation on all rails was pretty tight with the +12V rail registering a close to 1% deviation. Finally, the fan was spinning at full speed after 50% load. The noise it produced at 50% load wasn't annoying, but it surely wasn't silent either.
As you can see, the PSU easily delivered a higher-than-its-max-rated-capacity load by keeping the rails close to their nominal voltages. Also, the attained efficiency at 110% load was very high and exceeded 89%.
Such positive overpowering results should not encourage anyone to do the same to their PSU. Overpowering your PSU greatly shortens its lifespan. Some units don't behave as well as the G-550 while overloaded, registering high ripple, loose voltage regulation etc. Simply buy yourself a stronger PSU if you think your system needs more Watts. Do not overload your current unit.