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. The AC source is a Chroma 6530 capable of delivering up to 3 kW of power. We also used a Rigol DS2072A oscilloscope kindly sponsored by Batronix, a Picoscope 3424 oscilloscope, a Picotech TC-08 thermocouple data logger, two Fluke multimeters (models 289 and 175), a Keithley 2015 THD 6.5 digit bench DMM, and a lab-grade N4L PPA1530 3-phase power analyzer along with 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 three more oscilloscopes (Rigol VS5042, Stingray DS1M12, a second Picoscope 3424), and a Class 1 Bruel & Kjaer 2250-L G4 Sound Analyzer we equipped with a type 4189 microphone that features a 16.6-140 dBA-weighted dynamic range. You will find more details about our equipment and the review methodology we follow in this article. We also conduct all of our tests at 40°C-45°C ambient to simulate the environment seen inside a typical system more accurately, with 40°C-45°C being derived from a standard ambient assumption of 23°C and 17°C-22°C being added for the typical temperature rise within a system.

We use a GPIB-USB controller to control the Chroma 6530 source, which avoids its incredibly picky Serial port. This controller was kindly provided by Prologix.



To protect our very expensive Chroma AC source, we use an OLS3000E online UPS with a capacity of 3000VA/2700W.

Primary Rails Load Regulation

The following charts show the voltage values on the main rails, recorded over a range from 60 W 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 loads we throw at it.

Hold-up Time

Hold-up time is a very important PSU characteristic and represents the amount of time, usually measured in milliseconds, a PSU can maintain its output regulations as defined by the ATX specification without input power. In other words, it is the amount of time a system can continue to run without shutting down or rebooting during a power interruption. The ATX specification 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 PSU failed this test. A larger bulk cap would definitely offer better results, but it would also decrease overall efficiency.

Inrush Current

Inrush current, or switch-on surge, refers to the maximum, instantaneous input-current drawn by an electrical device when it is 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 a PSU's inrush current right as it is turned on, the better.



Inrush current was very high despite the large NTC thermistor.

Load Regulation and Efficiency Measurements

The first set of tests revealed the stability of the voltage rails and the V750's efficiency. The applied load was equal to (approximately) 10%-110% of the maximum load the PSU can handle, in 10% steps.
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 the +12V rail can handle while the load on the minor rails is minimal.


Load regulation on the +12V and 5V rails is satisfactory; however, the VSM550 performs better here. We expected deviations to be much lower at 3.3V. Only the 5VSB rail managed to outperform the VSM550. The changes to the platform obviously failed to improve load-regulation, even affecting it adversely. The V550 is pretty efficient with low- and mid-level loads; however, efficiency dropped significantly as the load increased, which lead to a reading below 90% at full load. The PF readings were quite low in all these tests.

The V550 was very quiet at up to the 50% load test; however, its fan spun significantly faster at higher loads, which nearly doubled its output noise. The fan is quite loud at full speed, which didn't surprise us since 120 mm fans need to rotate at high speeds to produce enough airflow.