What is the best 720-750W Power Supply?

Seasonic X-Series 750W Review

Manufacturer: Seasonic
UK price (as reviewed): £124.50 (inc VAT)
US price (as reviewed): $139.99 (ex Tax)

Like FSP, Seasonic is primarily an OEM manufacturer that supplies various brands with its products. It's also renowned for a range of high quality PSUs that retail under its own name, one of which is the X-750 that forms part of its recently revamped X-Series. It sports 80 Plus Gold certification and at £125 is on the expensive side, but the seven year warranty that accompanies the X-750 demonstrates the faith Seasonic has in its PSU.

The black chassis is relatively plain but with a gold font used for the logos and writing, which we rather like. A honeycomb mesh makes up the intake and exhaust areas, with cooling supplied by a 120mm fan. As with the PC P&C PSU, this can be toggled between normal operation and a hybrid, semi-passive mode.


The X-750 is one of just two fully modular PSUs on test, with even the main motherboard cable detachable - for what that's worth. Thankfully, despite all looking pretty similar, each of its cable holes are clearly labelled so there shouldn't be any mistakes. The main ATX connector is sleeved and rounded, while the remaining cables are all completely black and use a flat design. The healthy array of connectors includes five molex, ten SATA and four 6+2 pin PCIe ones. Though the SATA and molex cables are comparatively quite short, the remainder are perfectly reasonable lengths.

Sticking to a single rail design, the X-750 is able to supply nearly its entire total rated capacity along the 62A +12V rail. In terms of voltage stability, this is one of the strongest PSUs, with each of the output readings on every rail being close to the ideal values, and easily within the Intel limits.

What's especially impressive about this power supply is that despite it lacking the 80 Plus Platinum certification of the Enermax one, it still comes out overall as the most efficient PSU on test. It's average efficiency is a massive 91.6 percent, with its peak efficiency of 92.13 percent under 500W load also making it the only PSU on test to score above 92 percent in an efficiency test.

Ripple performance is also very favourable, as its highest value is just 53.2mV on the +12V rail in the 700W load test, which places it just a fraction behind the top place Enermax. It is possible to achieve even lower ripple values, but being consistently below 55mV is still an excellent achievement.

Without load, power usage from the Seasonic PSU is just 0.2W. Meanwhile, the noise levels test again demonstrates the benefit of a semi-passive fan mode - engaged via a sturdy switch on the PSU's front. Like the Silencer MK III 750W, the X-750 stays cool enough so as to not need its fan even after 20 minutes of a 500W load test, so you can expect it to remain silent for the majority of the time you use it.

Technically speaking, the electrical tests make the Seasonic PSU the best one of the round-up. Its fully modular cable set, silence under heavy load and seven year warranty are the cherries on top, and it does a good job of justifying its £125 price tag. However, as the final supply in our test - XFX's offering - demonstrates, it's possible to strike an even better balance between price and performance.