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, 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 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 TP-750's hold-up time was spot on. This is of note since most of the PSUs we have tested so far failed this test. You see, APFC caps don't come cheap and their capacity can decrease the unit's efficiency, which makes picking the right cap for the APFC converter a tough call.

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.



This PSU's good design kept inrush current low. We didn't expect anything less from Seasonic.

Voltage Regulation and Efficiency Measurements

The first set of tests revealed the stability of the voltage rails and the efficiency of the TP-750C. 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. We dialed the maximum load the +12V rail can handle while the load on the minor rails was minimal in the second test.

The TP-750C easily delivered more than its full capacity at very high ambient temperatures, which proves that it can deal with excess heat. We never had any doubt since it uses nothing but Japanese caps rated at 105°C. Regarding performance, the unit scored a pretty tight voltage regulation on all rails, and its efficiency was high enough, although not as high as Gold-certified high-end PSUs. The reason for its slightly lower performance is the semi-synchronous rectification scheme in the secondary side, where the used SBRs aren't as efficient compared to active components (mosfets). However, the TP-750C doesn't belong at the very top, and its efficiency is excellent for its category.

The PSU produced a lot of noise with 60% load and above - its fan actually cracked 50 dBA in our tests. The TP-750C requires a lot of cooling since the rectifying mostfets and SBRs are on the mainboard, not a heatsink, which translates into more noise.

We should also add that once we finished the overload test, which pushed the unit really hard, the PSU's Over Temperature Protection kicked in to shut it down (right as we removed the load). Turning it on after letting it cool down for a short time was not a problem.