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 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, 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 over a range of 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 with the 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 registered hold-up time was less than the limit the ATX spec specifies. The unit apparently needs a bigger bulk cap, but these cost enough, so manufacturers usually try to reach the 16 ms hold-up time with a load of 90% or less, which isn't in line with the ATX spec.

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, relays, and bridge rectifiers; as a result, the lower the inrush current of a PSU right as they are turned on, the better.



The small bulk cap has an advantage here, causing registered inrush current to be quite low.

Voltage Regulation and Efficiency Measurements

The first set of tests revealed the stability of the voltage rails and the efficiency of the L8-500W. The applied load was equal to (approximately) 20%, 40%, 50%, 60%, 80%, 100%, and 110% of the maximum load that the PSU can handle. We conducted two additional 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 0.10 A. This test reveals whether the PSU is Haswell ready or not. 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 unit managed to deliver its full power at 45°C ambient; however, we encountered shutdowns due to OTP (Over Temperature Protection) at the same operating temperature during the 110% load test. That said, we operated the PSU outside of its limits and can't blame it for such behavior. It did its job just fine because its protection circuits worked properly, saving it from burning up as its official specs set 40°C as the maximum operating temperature.

Voltage regulation is tight for a mainstream PSU, and efficiency is at acceptable levels for a Bronze unit with 230 VAC input. Without any doubt the most impressive part is the silent operation of the unit under such tough conditions as those we conduct our tests in. The fan barely exceed 38 dBA noise at worst, making normal ambient almost inaudible unless you have Superman's hearing.

Regarding Haswell compatibility, the results of the CL1 test clearly showed that this unit doesn't meet the requirements Intel set. The 5V rail went out of its limits, but its performance in this test and under these conditions was still quite good for a group-regulated PSU. Also, the +12V rail increased its voltage significantly, but it was still within the specified range.