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 can deliver 2500 W of load, and all loads are controlled by a custom-made software. We also used a Rigol DS2072A oscilloscope kindly sponsored by Batronix, 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. We even had three more oscilloscopes (Rigol VS5042, Stingray DS1M12, and a second Picoscope 3424), and a CEM DT-8852 sound level meter at our disposal. You will find more details about our equipment and the review methodology we follow in this article. We conduct all of our tests at 40°C-45°C ambient to simulate the environment seen inside a typical system with a higher accuracy, 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.

Primary Rails 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 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

Hold-up time is a very important PSU characteristic and represents the amount of time, usually measured in milliseconds, a PSU can maintain output regulations as defined by the ATX spec without input power. In other words, it is the amount of time the 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.



Typical to most PSUs we have tested so far since large bulk caps increase both cost and lower efficiency, hold-up time didn't reach the minimum time the ATX spec sets.

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 it is turned on, the better.



Though still on the safe side, inrush current was, compared to other 750 W units, on the high side.

Voltage Regulation and Efficiency Measurements

The first set of tests revealed the stability of the voltage rails and the efficiency of the ST75F-GS. 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 the +12V rail could handle while the load on the minor rails was minimal.

With 20% of the maximum-rated-capacity load, efficiency is low for a Gold unit, but it surpassed 91% in the next tests and only fell marginally under 90% during the overload test (110% of maximum-rated capacity). We have seen Gold PSUs register significantly higher efficiency, but can't call this PSU's efficiency results low. They are average for this category. Voltage regulation on the +12V and 5V rails is within 2% and within 3% on the 3.3V rail. Only voltage regulation on 5VSB rail exceeds 4%. Silverstone's promise for deviations of up to 3% on all three major rails then stands.

This PSU had no problem operating at very high ambient temperatures, although its cooling fan spun at full speed under such tough conditions, which produced a ton of noise because the lack of a beefy heatsink in the secondary side tasked the fan to run at full RPM to produce a lot of airflow. Take into account the PSU's low maximum operational temperature and its aggressive fan profile becomes a must. A different approach to the design could significantly reduce noise output since Gold certified units produce less heat than lower efficiency PSUs.