Seasonic X-400FL Platinum 400W Power Supply Review

This new Seasonic PSU touts Platinum efficiency, a fully modular design, and a host of other enthusiast-worthy hardware features that will ring true with those looking for a what might be "the best" 400 watt PSU on the market. For those of you looking to build that truly powerful HTPC, this PSU also offers silent operation.



The Seasonic X-400FL Platinum is the newest in a long line of power supplies we have seen from Seasonic based on its original X-Series design. This particular unit happens to be the second fanless model we have seen and only the 4th fanless unit we have seen total. To date, all of the Seasonic units based on the X-Series designs have been excellent and all of the fanless units we have reviewed have been excellent as well. As such, the X-400FL Platinum surely has a bit of work ahead of it. Is it up to the task? Or are we finally going to see a Seasonic unit choke in testing? Let’s move on and see.

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-400FL Platinum is simply excellent across the board as it was with the X-400FL and many other units derived from the X-Series design. Cosmetically, the unit is identical to the X-400FL save for the changes in accents which denote this unit as the Platinum version. This similarity includes the heavily perforated casing in order to aid in cooling. Oddly, the cables are a good bit longer than what we would expect from a unit that is supposed to be geared towards HTPC type applications but this was the case with the X-400FL as well so it seems to be way Seasonic is going to be doing things with this kind of unit. When we look to the interior of the unit, we find that it is once more exceptionally well built and a very modern design filled with excellent components. The design varies in slight ways from the original X-400FL but all of the variances are things that we have seen in the Platinum-660 and/or the recent X-850. The capacitors are again provided by Nippon Chemi-con which is excellent and these cover both the primary side and the secondary side. Otherwise, all of the excellent features and build quality points of the X-Series based units can be found again on this unit. In addition to all of that, this unit comes backed by a 7 year warranty which is a full 2 years longer than what we saw on the original X-400FL.

Load Testing

The load testing results for the Seasonic X-400FL Platinum at 120v and 100v were outstanding and in a number of ways better than what we saw from the previous X-400FL. The voltage regulation for the X-400FL Platinum was excellent as we saw a total change of just 0.07v on the 12v rail and a change of just 0.04v on the 5v rail followed by a change of 0.03v on the 3.3v rail. These results are a bit mixed compared to the X-400FL but trending to the better. One area where this unit does cleanly best the X-400FL is in the efficiency values which ranged from 90.20% to 93.53% at 120v and 89.29% to 92.70%! As with the previous X-400FL, these results are some of the best that we have seen among its peer group. Before moving on, we should say that the unit also easily passed the 80 Plus Platinum testing as it was 90.48%-93.37%-91.13% efficient using 80 Plus’s load testing parameters which is often not what we see with retail units..

With the previous X-400FL, the Transient Load Testing was one of the weakest points of that unit. Today, however, the X-400FL Platinum shows a good bit of improvement in this area. The loaded 12v rail saw peak changes of ~280mV while the 5v rail saw a peak change of ~100mV when directly loaded. While we have seen some better results than this from a few other units, this unit is just a 400W and, as such, the transient loads represent a much larger portion of this units capacity than it does for larger capacity power supplies. Given that, and the fact that this unit improves upon its predecessor we have no real qualms with not only declaring this a passing result, but also a very good result.

DC Output Quality

The Seasonic X-400FL Platinum passed the DC Output Quality tests today, and did well, but this is one test where this unit did do a bit worse than its predecessor. During load testing, the previous X-400FL managed to post peak trace amplitudes of just ~20mV on the 12v rail and ~10mV on the minor rails. Today, we saw the X-400FL Platinum match the minor rails result but the 12v rail posted a peak trace amplitude of ~35mV. While the change is just ~15mV, it is also almost double the value we saw with the previous X-400FL and not exactly the direction we would like to see things going. Still, at ~1/4 of the ATX12v specification limit it is a good result, but just not quite the impressive showing we saw 3 years ago with the X-400FL.


The Seasonic X-400FL Platinum is fanless, which, unsurprisingly, made this unit silent.

Paul's Thoughts:

Power supplies like the Seasonic X-400FL Platinum are likely never going to be anything but niche products due to price and limitations. However, the silent niche is certainly one of the bigger niches to aim for and one where the connoisseurs of such a product are demanding of perfection. The previous X-400FL was definitely something that met most of the demands of this niche when we saw it 3 years ago, which is certainly commendable. Today, the X-400FL Platinum that we see is essentially a replacement for the X-400FL as, while it does do better in most aspects than the X-400FL, nothing today is as revolutionary as the results were for the X-400FL when it debuted. Being an equivalent quality replacement is not necessarily a bad thing under those circumstances, particularly when there really are very few things that can challenge this unit and the previous unit did do so well, there just isn't that same initial sense of awe at something coming out of left field as before. That said, one of the best things that this unit has going for it is that, while not being revolutionary, it is evolutionarily at a price point lower than what its predecessor debuted at with no real other competitors at this capacity. I am sure we can all agree that slight improvements overall and a lower price point is certainly something we can get behind.

The Bottom Line

The Seasonic X-400FL Platinum is a product which will have limited appeal as it is a niche product like the X-400FL before it. However, while niche products often make compromises in order to fulfill the particular niche, the X-400FL made few compromises before and the X-400FL Platinum makes even fewer today because of one important aspect; price. Before we get to that though, we have to touch on this unit’s performance which was simply excellent. The X-400FL Platinum posted excellent load testing results, some of the best efficiency we have seen to date, excellent DC output quality, silence during testing, and excellent build quality. Among these data points, we have to point out that the X-400FL Platinum was better than the X-400FL when it came to the load testing, Transient Load Testing, and efficiency but did trail the X-400FL when it came to the DC Output Quality. Now, that said, this unit is clocking in today at a price of $119.99 with Free Prime Shipping. That is less expensive than where the X-400FL came in at when it released and it is worth mentioning again that this new unit has a warranty that is two years longer as well weighing in at 7 years. In that context, while the X-400FL Platinum may not be a revolutionary product, the X-400FL Platinum is better than its predecessor overall and it is less expensive which is something that makes it certainly worth consideration by users looking for a solid silent power supply.

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Seasonic X-400FL Platinum 400W Power Supply

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