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Seasonic's X Series 750W
One of its very own

Manufacturer Seasonic
Model X Series 750W
Price (Street) $179.99
Availability Now

Seasonic is one of the largest PSU manufacturers around. In fact, Seasonic builds PSUs for a good number of other firms that then sell those units under their own names. The X Series is Seasonic's very own product, though, and its most advanced model to date. This is the first power supply we've tested with 80 Plus Gold certification, too—the highest standard the program sets for ATX PSUs.

The X Series carries a bit of a premium thanks to its Gold certification; the 750W model costs $20 more than Corsair's HX750W. The Seasonic unit is also considerably harder to find online. Our price search engine doesn't list it, but Newegg does have units stock, with free shipping, to boot.


Seasonic PSUs have never been particularly flashy, and neither is the X Series. The combination of matte black with gold trim reminds me a little of old-school stereo equipment for some reason. The look is a classy one, although there's less of it, simply because the X Series is the shortest PSU of our pack by about an inch. None of the PSUs in this round-up are too large to squeeze into most mid-tower cases, though.

Perhaps because the X Series has a smaller casing, Seasonic uses a Sanyo Denki San Ace fan that measures just 120 mm across. This is the smallest fan in the bunch. Still, given Seasonic's pedigree, it's hard to question the decision. Seasonic's focus seems to be on lower noise levels, which is why the fan doesn't spin up at all until the PSU is loaded up to at least 20% of its capacity. From there, the fan spins at a constant "silent" speed until the PSU load reaches 50%, at which point the fan really starts to ramp up.


Internally, the X Series uses a patented DC connector module with an integrated voltage regulator that the company claims offers "near perfect" DC-to-DC conversion for 3.3 and 5V power. According to Seasonic, this design allows the PSU to run lower currents to supply its 3.3 and 5V lines, reducing loss and improving overall efficiency.

All of the PSUs in this round-up may be modular, but the X Series is the only one that's completely so. Each and every one of its cables, including even the primary motherboard connector, can be completely detached.


While this arrangement may offer questionable utility for end users who are probably always going to need a primary motherboard and auxiliary 12V line connected, the lack of attached cables does make the X Series a little easier to squeeze into tighter enclosures. The cables are nicely sheathed, too—not just down to the first plug on each line, but in between the subsequent ones, as well.

The X Series 750W offers consistent DC voltage delivery that's well within the company's +/- 3% tolerances.

AC ripple is low, as well, averaging about 50 millivolts across all rails and load levels.

Like the HX750W, the Seasonic X Series is most efficient under the lightest load generated by The Beast. There's little difference in efficiency between loads at 50, 75, and 100% of total capacity.