Seasonic X Series: X-750 Power Supply Review

Fully modular, 750 watts of computing power, high efficiency, and a great build quality has been done before in the world of PSUs, but never quite like this. Seasonic's X Series is an evolution in the world of power supplies.



The Seasonic X-750 is the third Seasonic built power supply we have seen to date that is being sold under the Seasonic brand but far from the third we have seen overall given the their role as a major quality OEM provider of power supplies. The first two Seasonic built and branded power supplies we saw were everything Seasonic is known for, efficient, quiet, and powerful (for their output capacity). Remarkably, even when jumping up to 850W's with the M12D-850 Seasonic still hit all of its key features and knocked one out of the park. As such, today’s 750W entry seems like it should be a shoe-in for excellence given everything else we have seen from Seasonic. But is it time for an upsetting of the order of things with Seasonic? Or is Seasonic going to keep on running the table on us?

HardOCP’s testing methodology is intended to very much push power supplies to their advertised wattage rating in temperatures that will represent some of the hottest computer enthusiast cases. So if a unit passes all our testing it is definitely not something to take lightly. In fact we expect more power supplies to fail our testing than make it through unscathed.

Build Quality

The overall build quality of the Seasonic X-750 is excellent across the board in really every way. There simply were no times when this unit did not scream quality. The exterior of the unit is well trimmed with a flat and slightly textured rugged black finish. The accents used on this unit were all subtle and elegant for those of you with windowed cases. The interior of the unit provided us with one of the most unique designs we have ever seen and was extremely well thought as this design really frees up a lot of space inside the unit to improve airflow (among the other benefits of the new design). The integration of the unit was also rock solid. The PCBs have some of the best soldering we have seen to date, and the connections to the modular interface are certainly a different approach that helps out on a number of fronts. This is all combined with another round of excellent component selection as the secondary is filled with solid capacitors from Nippon Chemi-con and the primary features a pair of standard electrolytics from Nippon Chemi-con as well. Beyond that, the unit also featured a solid manual (though it could always be a bit better) and a 5 year warranty which is good to see. All in all, this is an awesome package from Seasonic when we look at just the build quality, integration, and attention to detail.

Load Testing

The Load Testing results for the Seasonic X-750 were generally excellent across the board as well. We see that the voltage regulation for the X-750 was good overall with the biggest change being on the 12v rail as it dropped 0.21v over its entire capacity while the minor rails dropped between 0.05v and 0.06v. Those numbers were good, and repeated at both 120v and 100v but what this unit has been marketed as is efficient. Not just a little efficient, but 80lus Gold efficient which is 87%-90%-87% at 20%-50%-100% load at 25C. What we saw today was not just 80Plus Gold, but 80Plus Gold numbers at our own sweltering testing conditions of 45C ambient temperature. That is right, the X-750 managed to be 87.50% to 90.07% at 45C and 120v input and even hit 86.44% to 89.21% at 100v and 45C. These are AMAZING results, and certainly this unit has lived up to that part of its billing and then some.

However, no unit is perfect and the biggest blemish for the X-750 today comes from its Transient Load Test results. Specifically the loaded 12v rail which dropped by ~340mV when loaded. This does not compare so favorably to the last 750W Seasonic unit we saw, the PC Power & Cooling Silencer 750 Quad CrossFire, which dropped by just ~200mV. When we look at the 5v rails results we see better results than for the 12v rail as it peaked at ~80mV when loaded which is within the realm of expected results (and beats out the Silencer barely). So the unit was not across the board weak in this regard, but the 12v response was certainly not desirable compared to that earlier (and more traditionally designed) unit. In the end though, the unit did pass so while not as good as we would hope for this was not a deal breaker for the X-750.

DC Output Quality

The DC Output Quality of the X-750 quite clearly shows us that the X-750 is a masochist. Yes, the harder you beat on the unit the better it does overall. Clearly, this unit has good DC Output Quality overall as it peaked at just ~35mV on the 12v rail and ~20mV on the minor rails but that 12v peak was in Test #1. Once we put the screws to the unit the 12v trace amplitudes dropped to ~10mV or below and never came back up. This was true through all of our testing. The 12v rail just likes the abuse. The minor rails showed the usual pattern of small increases as their load increased but they too did well as stated above. As such, the DC Output Quality of the X-750 was very good at low loads and phenomenal when it was really put through its paces which should be of real interest to our overclockers and high end system builders out there.


Like with the efficiency angle, Seasonic has spent a lot of time advertising the noise (or lack thereof) associated with these new X Series units and Seasonic really has been one of the leaders in this regard for some time. Physically, the X-750 is very efficient, has a single overhead 120mm fan, an interesting fan controller, and features a design that really reduces the clutter inside of the unit so that cooling the unit can be done at much lower volume levels. That is, if everything works as designed. And work as designed this unit did. At no time during testing did this unit make even a peep. In Test #1 the unit’s fan did not even turn on and even by Test #4 when the fan was running at its full tilt the unit’s exhaust was still well in check with no apparent noise being emitted. Certainly the unit is not silent as in 0 dBA silent, but it was seemingly silent in all of our testing. This includes even when working with the unit out of the incubator as it made no real noise there either. Really, any other fan or pump in your system is likely going to be louder than this power supply ever will be.

Paul's Thoughts:

What is there not to like about the Seasonic X-750? Really? It surpasses the advertised efficiency standards, is ridiculously quiet, has great DC output quality under load, and is amazingly well built. When you go about reinventing the wheel you generally don't get an initial product that looks this good. Generally, you have to work on things a bit to get everything right and while there are a couple points that could be improved on with the X-750 it absolutely delivers on everything it advertised and then some. Sure the Transient Load results could be better and sure the 12v voltage regulation could be a bit tighter, but in the context of what the X-750 offers these things are inconsequential. I am not sure if I can reiterate it enough but very few products I see floor me, and floor me this unit did. There was so much new and interesting here with the design that it made this unit a dream to work with and really unique to handle. To top it off the unit then performed better than expected and better than advertised. This is the kind of experience users should expect from premier products no matter if it is a motherboard, videocard, or power supply. Any product carrying a premier price tag such as this should "WOW!" you, and be worth every penny of that price, and the X-750 "WOWs" in a way that makes it worth every bit of its premium price tag.

The Bottom Line

The Bottom Line? The Bottom Line is that users should have but one question about the Seasonic X-750. Do I want ground or accelerated shipping on my order? The X-750 is the real deal and provides users with an efficient, stable, well regulated, amazingly well built, and superbly quiet basis to build any system around. Be it a HTPC or a high-end gaming rig the X-750 can do it all and do it all well. This power supply is quite simply one of the most exciting products that has crossed our test bench (and not exploded) in quite some time. The Seasonic X-750 PSU is close to perfection on almost every front. At a price of $199.99 (MSRP) this unit may seem pricey for 750W but you get what you pay for and then some with the Seasonic X-750.

We were expecting this unit to be for sale today through Newegg, but there have been some holdups. We expect the Seasonic X-750 to be selling at Newegg very very soon.

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Seasonic X-750 Power Supply