ProsAmazing "power-to-weight" ratio; highly-tuned fan profile provides truly silent cooling; ultra-efficient
ConsNo ATX adapter included in the box; ideal use case is extremely limited; ultra-expensive
Here at The Tech Buyer's Guru, we've tested a lot of power supplies. But this is our first published review, and we've held off on reviewing power supplies until now for a reason: we don't have (and do not intend to purchase) the advanced load testing equipment required to assess the electrical properties of power supplies. That's just a bit too far out of our range of expertise. And anyway, most high-quality units (read: everything other than bargain-basement offerings) will pass all the required efficiency, voltage regulation, hold-up time, and current tests required to achieve their relevant "80 Plus" certification. In fact, unlike so many other components in the PC industry, power supplies are very well regulated, which means it's hard to get a real lemon. And that's a good thing, because a bad power supply can take down an entire system pretty quickly. So what we're going to focus on in this review (and future power supply reviews) is price, fan operation, noise, and overall utility.
And all of those criteria are particularly important for the power supply we're testing here, SilverStone's new SX700-LPT 700W Platinum-rated SFX-L power supply. SilverStone essentially created the market for SFX PSUs back in 2010. Prior to that, SFX units were only available in barebones systems, but SilverStone decided to market the SFX PSU as a retail product with the release of the SilverStone ST45SF. This coincided with its release of a number of its ground-breaking case designs that needed SFX PSUs, like the impressively-compact SG05. It then carved out a new market for itself with its SX500 SFX-L power supply, introduced in early 2015, which took the SFX concept and stretched it (literally!) just enough to fit a 120mm fan. And this was a critical step, because a bigger fan is almost always going to be quieter when providing the equivalent amount of cooling as a smaller unit.
We say "almost," because in all honesty, SilverStone goofed up with its SX500. It used a PWM fan designed to run at certain RPMs, and then forced it to run in a zero- and low-RPM mode that just didn't work well. You see, PWM fans are typically not designed to spin near 0 RPM, or anywhere close to that, and running them at low speeds causes them to spin off balance. And thus, the SX500 was loud and obnoxious under light loads, but pretty tolerable under heavy loads. We tested two samples, neither was good, and we pulled all recommendations of the unit off this site in May 2016. Unfortunately, that was too late from our point of view, as we don't like recommending products that we wouldn't buy again, and we definitely would not give the SX500 a third chance at the plate.
All that changes today with the SX700, a more expensive, more refined, and yes, much quieter power supply than the SX500. In this review, we'll share our thoughts on why SilverStone's second attempt at designing the ultimate compact power supply is such a success story! Update: After this review went live, SilverStone provided us some helpful information on the issues facing the original SX500. It is planning on releasing a "V2.0" of the SX500-LG, which will remove the semi-fanless function so the fan can start normally and run within its intended voltage range. Our advice is to wait for the V2.0 if considering the SX500.
We'd like to extend a special thank you to SilverStone for providing us a review sample of the SX700-LPT.
Description and Features
First off, being an SFX-L power supply, which is a form factor so far exclusive to SilverStone, the SX700 is 125mm wide, 63.5mm tall, and 130mm long. The only dimension that differs from SFX units, like Corsair's class-leading SF600, is the length, which is 30mm longer than the SFX standard. As mentioned above, the main benefit of this extra length, in addition to more space for internal components, is the ability to use a high-efficiency 120mm fan, rather than a 92mm fan like Corsair's unit, or the 80mm fans of many of SilverStone's earlier SFX models. Larger fans can provide the same or greater cooling capability at lower noise levels than their smaller counterparts. The big 120mm fan essentially fills the entire top panel of the power supply, making an impressive visual statement.
The SX700 differs from its SX500 forebear in a number of ways, but the most obvious is the number of power cables it supports. Rather than three SATA connectors, it has four, and instead of one PCIe cable (with dual 6+2 pin connectors) it has two PCIe cables. These in turn provide a total of four 6+2 pin PCIe power connectors, which would support two ultra-high-end video cards, or one of the very rare cards that uses three PCIe power inputs.
And this is where we raise our first major concern about the SX700. Sure, it's an impressive feat to provide 700W and four PCIe power connectors in such a small form factor, but finding an application for this power is like finding a needle in a haystack. Among all our Small Form Factor Buyer's Guides, there isn't a single build that requires 700W. And while we do recommend 650W units from time to time, these are always cheaper ATX models.
Now, there's of course an argument to be made for using an ultra-efficient, ultra-compact, ultra-quiet power supply in an mATX or ATX chassis, even if it comes with a price premium, as does the SX700. But SilverStone throws a wrench into those plans by omitting the extremely useful SFX-to-ATX adapter that it included with the cheaper SX500. This move completely baffles us, and we strongly believe it's something SilverStone is going to want to remedy as quickly as possible. As we'll show on the next page, the SX700 offers truly stellar performance, but given its $150 retail price and its massive power output, we believe the right target audience will be builders putting together compact dual-GPU mATX systems. And yet, as it stands, they can't use this power supply out of the box. That's a real shame from our point of view.
We have just a couple of other observations about the build quality and layout of the SX700 before we turn to performance. The exterior of the SX700 is finished in a black matte paint, nothing too flashy, but at least it's high quality and unlikely to chip. We don't disassemble PSUs, as it's not something we believe should be necessary to use a PSU (and in fact voids the warranty), but we can note that the topography of the circuit board on the SX700 allows for a lot of open space near the fan intake, but conversely a very crowded exhaust vent area. Over half of the rear panel is in fact blocked by circuitry or switches, which generally isn't great for keeping temperatures low. But this unit is Platinum-rated, after all, so perhaps SilverStone is confident enough in its efficiency to assume that there just won't be a lot of waste heat to exhaust.
All right, with the description and features covered, we'll move on to what really makes this power supply stand out: its performance!