The Seasonic Prime Fanless TX-700 is a new but quite expensive passive power supply bursting with superlatives. And yet there is a seemingly fundamental design problem that the layman cannot detect in this way and that can nevertheless lead to consequential damage to the connected hardware. Of course, I don’t want to anticipate the detailed review of my friend Aris Mpitziopoulos (Hardware Busters), which will soon be published in full length by the esteemed colleagues of Techpowerup. Still, since the YouTube video of Aris is already online, I agreed with him to summarize at least the most critical facts in advance for the German readers with his kind permission.
However, the case is a bit different from Gigabyte’s P750GM, whose verifiable vulnerabilities I pointed out in an article “Fireworks in the PC and purchase warning: Gigabyte’s current P750GM power supplies affected by total damage” and for which Gigabyte Germany punished me with love withdrawal instead of actively addressing the issue. While the main issue with the P750GM was that the power supply could self-destruct with a bit of bad luck and a real fire risk, the problem with the Prime Fanless TX-700 is a bit deeper and concerns the stability and the lifespan of the connected components.
It’s just that then, as now, I cared more about the well-being of the readers and potential buyers of the hardware than the sensitivities of PR staff. Of course, one must always prove such things, so I first discussed with Aris in detail how we could handle today’s article. It is always important to remain objective in such matters and avoid sensationalism. The truth is not always tender and gentle, but in the end, unfortunately, only the pure facts count. I’m sure Seasonic will be proactive here (as they have in the past) instead of sitting out problems. This, of course, is another thing that separates a real manufacturer like Seasonic from companies that merely re-label things they buy in, leaving themselves helplessly at the mercy of even the lower-priced OEM/ODM.
The TX-700 in the test
Seasonic offers two fully passive Titanium-efficient power supplies, the TX-600 and the TX-700. Not many manufacturers dare to bring fully passive power supplies to the market because of the design and manufacturing difficulties. In addition, the TX-700 is the most powerful passive power supply available on the market today. The most efficient way to build a passive power supply is to implement overkill on each component, leave many watts in reserve (headroom), and increase efficiency as much as possible to keep the thermal load low. That’s exactly what Seasonic did, so good on them.
Also, the heat must be able to easily dissipate from the PSU’s case, so it must either use large heatsinks to dissipate the heat or be designed with many holes like Swiss cheese (see picture above). It is also essential that you do not install a passive power supply in a way that blocks the flow of hot air. The Prime TX-700 should therefore never be installed sideways or with the bottom side facing upwards, as otherwise, the hot air will accumulate inside the case. Up to this point, everything is unsuspicious and in order. But this is nothing new and has nothing to do with today’s topic.
Aside from the overall performance of the actual potent TX 700, as well as the lax load regulation on the side rails and mediocre transient response, Aris’ biggest concern with the Seasonic Prime TX-700 is rooted in the voltage drop he noticed on all rails during various power-up tests. Such high voltage drops are no small matter, and they can cause severe problems down the road, especially during the wake-up phase of a system or when booting from a powered-down state, where components require quite a bit of power to resume operation. But what does this mean in detail?
Specifically, in the Turn-On Transient tests and the PSU OFF to Full +12 V test, where a full load is applied to +12V as soon as the PSU is turned on, there is a notable voltage drop at +12V on the TX-700 that also affects the side rails as they are generated directly from the +12V rail. These voltage drops can lead to significant compatibility problems and they unfortunately put a massive strain on the mainboard’s DC-DC converters and other components, such as graphics cards, memory, etc. Aris tested a total of three, and they all had the same problem during this test. So it doesn’t seem to be an example-specific problem, but really a general design flaw.
Another problem that Aris has noticed is the very high turn-on time, which exceeds 100 ms. To avoid compatibility problems with mainboards, most manufacturers keep the power supply’s switch-on time well below 100 ms and ideally even below 50 ms. Finally, the lack of support for alternate sleep modes is another drawback of the TX-700. Because when you buy such an expensive power supply, you intend to keep it for several years. So it also needs to be as future-proof as possible.
I agree with Aris’ conclusion and recommend his entire video, which contains more details of his very in-depth test and a good summary. Of course, it’s not my place to criticize third-party PSU reviews that have already been published, but what Aris found really should have been noticeable to anyone who has not only touched the PSU but actually tested it. Whether it’s a YouTuber or conventional media, you can actually notice something like that. Again, I like to remind everyone of the pending review on Techpowerup.