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 a Yokogawa WT210 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, Rigol VS5042, Stingray DS1M12, and 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, with 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.

Primary Rails Voltage Regulation

The following charts show the voltage values of the main rails, recorded over a range from 60W to the maximum specified load, and the deviation (in percent) for the 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 the ATX spec without input power. In other words, it is the amount of time that the system can continue to run without shutting down or rebooting during a power interruption. The ATX spec sets the minimum hold-up time to 16 ms at maximum continuous output load. In the following screenshot, the blue line is the mains signal and 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.



The hold-up time does, as you can see, easily pass the minimum allowed limit that the ATX spec sets. It is, naturally, lower than the time that the AX760 scored on this test because the X-750 uses lower capacity caps in its APFC converter.

Inrush Current

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



The smaller caps in the APFC converter are, since both the X-750 and the AX760 utilize the same platform, responsible for the lower inrush current the X-750 registered compared to the AX760 unit.

Voltage Regulation and Efficiency Measurements

The first set of tests revealed the stability of the voltage rails and the efficiency of the X-750. 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 features a really cold operation, and we had to keep the heating elements of our hot box operational constantly in order to heat up the PSU. Regardless of the high ambient temperatures we achieved inside the hot box, the X-750 easily delivered its full power and even more while registering excellent voltage regulation and high efficiency. The PSU is actually capable of keeping all of its major rails within a deviation of 1% while registering efficiency levels that are amazing; reminiscent of high-performance Platinum units. We are pretty sure that this unit can clear the Platinum requirement at normal ambient, but Seasonic apparently didn't want to create internal competition amongst their Platinum X units. Finally, the fan didn't engage at all until the 40% load test even though the ambient inside of our hot box was high. Only after 40% did the fan increase its speeds, reaching audible noise levels at higher loads.