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 Class 1 Bruel & kjaer 2250-L G4 Sound Analyzer which is 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 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 Load 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 unit's hold-up time was very low, not only for a PSU of this price range and category, but for every ATX-compliant PSU. FSP probably sought to install smaller bulk caps in an effort to achieve the highest possible 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 the inrush current of a PSU right as it is turned on, the better.



Inrush current was normal for a unit of this capacity. However, given the hold-up time result, inrush current should have been lower.

Load Regulation and Efficiency Measurements

The first set of tests revealed the stability of the voltage rails and the PT-1200FM'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 could handle while the load on the minor rails was minimal.

With the exception of the 3.3V rail, load regulation was good overall, with the +12V rail staying within 1%. The large FSP unit was amazingly efficient by achieving well over 93.5% efficiency with typical loads, a performance level we don't see often with even high-end Platinum platforms. The PSU also easily delivered its full power at very high operating temperatures, and as you can see in the 110% load test, we pushed it very hard. Regarding output noise, the fan spun at very low RPM with up to 70% load, producing very little noise. To be frank, we initially thought there was a problem with the fan's circuit because ambient temperatures and load were well above the norm. Only in the 80% test did the fan start to rapidly increase its speed, producing a lot of noise in the last tests.

We also noticed something we hadn't encountered with other units thus far. Once a test finishes, we completely removed the applied load, and for an instance, the voltages on the rails increased to well above the norm. This happened repeatedly and was more apparent with high loads. This scenario is almost impossible to reproduce with an actual system since the PSU will always run a load, yet we would prefer it if the PSU were to behave normally in these simulated situations. The LLC resonant controller probably plays its part by responding poorly to the load's sudden and complete termination, given FSP's mechanics were right to assume that there are virtually no zero-load scenarios, and while this problem won't affect your system, seeing it resolved would be nice given strange reviewers like me tend to deduct performance points over such faults.