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 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), 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 three more oscilloscopes (Rigol VS5042, Stingray DS1M12, and a second Picoscope 3424), and a CEM DT-8852 sound level meter. 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 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 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 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.



The hold-up time easily exceeded 16 ms, which meets ATX spec requirements. This topology (ACRF) obviously allows for long hold-up times without the need of huge bulk caps which cost a lot and affect efficiency negatively.

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 the inrush current of a PSU right as it is turned on, the better.



Inrush current was especially low for a 850 W PSU.

Voltage Regulation and Efficiency Measurements

The first set of tests revealed the stability of the voltage rails and the efficiency of the Power Zone 850 W. The applied load was equal to (approximately) 20%, 40%, 50%, 60%, 80%, 100%, and 110% of the maximum load 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 can handle while the load on the minor rails is minimal.

Voltage regulation on the +12V and 5V rails was tight enough, and it was within 3% on the 3.3V rail, though there is still room for improvement. The ACRF topology isn't famous for its tight voltage regulation, but be quiet! managed to make FSP deliver a solidly performing unit in this area. The Power Zone 850 W's efficiency also isn't that of a Bronze PSU as its performance is more in line with that of a good Silver- or Gold-certified unit. It managed to score over 91% efficiency with typical loads and even did fairly well at full load.

The unit's fan had to work incredibly hard inside our hot box to keep temperatures under control, which produced a ton of noise. We expected be quiet! to use a more relaxed fan profile, but they were probably concerned about the unit's reliability over time given the mosfets that generate the minor rails are on the solder side of the main PCB, which means they are not passively cooled by the enclosure that often plays the role of a big heatsink in similar implementations. Some will argue that a modern system hardly puts a lot of duress on the minor rails; however, their combined capacity only reaches 160 W, which had engineers keep the worst-case scenario in mind.