Overclock.net › Components › Power Supplies › Silverstone SX700-LPT SFX-L PSU

Silverstone SX700-LPT SFX-L PSU

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Pros: Good power density, can power an SFF m-ATX rig, 120 mm fan + high efficiency helps keep it quiet

Cons: Expensive, slim fan used, 3 year warranty could be improved upon

This is going to be an abridged overview due to the limitations of the template here. The product was received from Silverstone via OCNLabs as part of the OCN reviewer program. The Silverstone SFX-L form factor SX700-LPT is a new PSU from Silverstone to cater to the small form factor which they have been a major participant in for years now. They remain the company offering the most choices of cases, PSUs and accessories for low volume builds, and this SX700-LPT arose as a need to improve upon their existing SFX series of power supplies which had small 80 mm size fans with an aggressive fan curve that resulted in relatively loud units. Corsair introduced the SF600 recently with a 92 mm fan and a better programmed fan curve accounting for both power draw and unit temperature that resulted in the need for Silverstone to come back with something they thought was better in all regards. Enter then the SX700-LPT with 700 W of continuous rated power draw, 80+ Platinum efficiency, and a 120 mm fan all within a slightly longer SFX-L form factor.

Unboxing, Overview and Internals

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The packaging is blue and white in color, with black writing to go along with Silverstone's usual color schemes. The company and product name is on the front along with an illustration of the PSU itself with specifications and marketing features on the other sides. A flap keeps the contents inside in place, and you see a multi-language installation manual along with a product manual with full specifications inside.

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A cardboard cutout next to the PSU itself keeps the cables in place, and there are a lot of them. Included also here are 4 installation screws but that's about it as far as accessories go. It would have been nice to see some cable management options provided via zip ties or otherwise, but I feel this is more on the case maker to provide than the PSU maker as it is. No SFX to ATX adapter bracket is provided in the box as well, and again I have no problems here given that the market is niche to begin with and including an accessory that very few will use while raising the product price for everyone is not a good idea in general. For those who do want one, Silvestone offers a PP08 adapter for an optional purchase.

The power cord is a good 5' (~150 cm) long, rated for 105 °C and uses 18 AWG wiring inside which is fine for 700+ W of power draw from the wall but it would have been nice to see a step up to 16 AWG wiring- especially since the unit can actually provide more than 700 W of power. More on that later. The PSU cables themselves are flat, ribbon style which seems to be the new trend in wiring these days. On one hand, it helps with costs that there is no sleeving done and the black insulation keeps things tidy while the flat nature of the cables helps with cable management in one axis. On the other hand, these cables will occupy more space in the other two axes compared to standard, loosed individual wire cables and can be tricky to maneuver around corners or do tight bends- a must for SFF builds. Thankfully, these cables are quite flexible and do allow for tight bends too, as demonstrated visually compared to a standard US quarter and had a bending radius measured at 0.45" which is slightly more than the cables on the Corsair SF600 but not enough to make a tangible difference.

The 24-pin ATX cable has a 20+4 split on the motherboard end which I am not a fan of. I would have preferred to have one solid connector to use in a potentially cramped area myself. It is 30 cm long and should suffice for most SFF cases. There is also a single 40 cm long EPS cable which is all I was looking for, and this is a 4+4 on the motherboard end allowing this to be used with motherboards that have a 4- or 8-pin EPS connector. Given this is a 700 W PSU, I would have been disappointed if there was no support for multi GPUs, and Silverstone does not disappoint. There are 2 PCI-E cables, with blue connectors on the PSU end so as to not be confused with the EPS cable/port, and both have a daisychained 6+2 connector on top of another 6+2 connector for a total of up to four 8-pin PCI-E connectors. There is enough power and cabling to power even more than 2 GPUs if you use an AMD RX 480 or Nvidia GTX 1080 reference GPUs (or similar) too. A neat touch here is that one of the cables is longer (55 + 15 cm) than the other (40 + 15 cm) to accommodate for one GPU further away from the PSU, and that will help with cable management as well. These 4 primary cables have 16 AWG wiring (lends even more credence to me wanting the power cord to use 16 AWG as well, but that's a discussion for another time).

On to the auxilliary cables now. Silverstone provides a single full size MOLEX cable with 3 MOLEX connectors for peripherals, pumps etc at a 30/20/20 cm length. There is also a 10 cm long MOLEX to Berg adapter to fit a floppy drive should you be so inclined, and thankfully it is an adapter and not part of a cable. There are also 3 separate SATA cables here which may be overkill for what the PSU is intended and advertised for, but at least you have choices. One is a longer cable with 3 SATA connectors at a 60/15/15 cm length, and the other two are shorter cables with 3 SATA connectors at a 30/20/10 cm length. Would omitting 1-2 of these cables have dropped the price of the PSU without reducing the user experience of the customer? Perhaps, but not by much. For those interested, Silverstone offers aftermarket cables- individually sleeves ones even- as does Cablemod via their new configurator.

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The PSU itself comes plastic wrapped and inside a 2-piece foam protection layer, and has a warning sticker alerting customers that the fan not turning on at idle is completely normal. This has a zero RPM mode in that the fan does not turn on and spin when under a certain temperature readout as measured by a sensor inside (which corresponds also to power draw at a set ambient temperature, 210 W at 25 °C for example). That aside, it is a sturdy little unit coming in at 125 x 63.5 x 130 mm conforming to Silverstone's own coined SFX-L form factor and longer than SFX PSUs by 25 mm. In practice, the extending modular connectors give another 3 mm of length protruding inwards (sans the protective caps) which users would want to be aware of. There are enough connectors for every single cable provided, including the two blue connectors fo the PCI-E cables. The PSU is a matte black in finish, with the Silverstone logo embossed on one side and the fan has a simple fan grill on top (no cutout on the casing itself) which will help keep air flow restriction low while still providing the protection needed. On the back is the power connector as well as an ON/OFF switch and a honeycomb style mesh with hex holes for optimum use of space while allowing hot air to exhaust out. Stickers on one side are indicators of certain tests having being successfully passed, as well as this being a version 1.0 unit and the load table is on the other side. The SX700-LPT is a single rail unit with 58.4 A on the +12 V rail, and the minor rails capable of 22 A each. The unit can also provide up to 15 W of stand by power which can help power USB devices, and perhaps even lighting on the motherboard or elsewhere depending on how they are powered. The PSU is also rated for an operating temperature range of 0-40 °C, so having good air flow is a must if you are working in a small, cramped case.

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The fan used to help cool the PSU is one that Silverstone has used in some of their other compact PSUs before, including the SX500-LG SFX-L PSU. It is a Shenzhen Power Year long life sleeve bearing fan, coming in at 120 x 120 x 15 mm. The impeller design is also not very unique in that many companies have used the same OEM for retail fans even, and slim fans typically tend to have more blades compared to thicker fans with this having 13 blades. The fan is rated for 0.22 A and powered by a 2 pin connector on the PSU for +12 V and ground (voltage control, no tach sensor). If you absolutely must swap fans for whatever reason, it must be a fan with similar dimensions and not drawing tremendously more power. Note also that you will have voided all warranty as well.

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High Power is the OEM here who Silverstone have worked with to bring the SX700-LPT to a reality. The two have worked together before on other compact PSUs under the Silverstone name, and have been a mixed bag when it comes to performance- especially with ripple suppression on the major and minor rails. But without access to a load tester, that remains to be seen how this PSU ended up performing. I recommend reading the PCPer review for more info on this and they were pleased with the unit overall. The insides are crammed with components here, with tall heatsinks and daughterboards present along with some relatively massive capacitors for an SFX style PSU, all of which are the reason Silverstone could not accommodate a 25 mm thick fan here. Beginning with the AC receptacle itself, there is filtering galore with y-caps, and also some Nippon Chemicon solid and polymer caps. The main PCB is held in place via 4 screws on the bottom but access to two of them was extremely hard in this case, and so good examination of the individual components was not possible. Soldering quality of the modular connectors daughter board was decent, but nothing special either.

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Silverstone helped me locate the three sensors that help measure temperature and also help control the fan/switch off the PSU. Sensor 1 in the image above forces the fan to run at power draw between 150-250 W if the sensor measures a temperature of 50 °C or above, meaning Silverstone has accommodate for some worst case scenarios here as well and above the rated 40 °C for the PSU. Sensor 2 helps regulate the fan speed during operation. Be it power draw which raises temperature read by this sensor, or just ambient temperature fluctuations, it ends up being temperature which controls the fan speed in the end. But it is fair to say that the fan speed is a function of ambient temperature and power draw as well here which is the way to go. Sensor 3 triggers over temperature protection (OTP) and shuts down the PSU if it measures a certain high temperature (not specified, but above 50 °C based off what sensor 1 does). All 3 appear to be NTC style thermistors, and they are all located on what I presume is the secondary heatsink.

Fan Testing

The stock fan in the SX700-LPT was tested in a 19 dBA anechoic chamber for noise measured 6" from the fan (intake direction) using voltage control fed manually using an Aquacomputer Aquaero 6 XT. No tach sensor pads were present on the fan PCB and so a non contact laser tachometer was used for RPM measurement, and an Extech 45158 Thermo-Anemometer was used to measure airflow through the PSU held next to the exhaust grill past the AC receptacle.

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Do note that these are the full spectra of RPM, noise and airflow for the entirety of the voltage control range for the fan, not necessarily what you will see during operation. That being said, we see that the fan was running at 1967 RPM at 12 V and went down to 542 RPM at 3 V before shutting down. I was expecting this to run faster given the slim design, but then again this may all that is needed given the high efficiency design in the PSU. For a comparison, let's see now how the fan in the Corsair SF600 tested:

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The 120 x 120 x 15 mm fan in the Silverstone SX700-LPT spins slower, is quieter and blows less air through the PSU compared to the 92 x 92 x 25 mm fan in the Corsair SF600. This makes sense once you realize that a 120 mm fan can blow a lot more air generally, and does not need to spin as fast thus making it quieter and why larger size fans are good when it comes to PSUs. The cramped interior in the SX700-LPT does hurt though, and airflow is less here even taking the much faster fan in the Corsair PSU (which is a lot less cramped).

Again, all this does not matter if the platform of the PSU and the fan curve used will not support it. Given it is a 700 W unit, I used an LGA 115x setup for power draw with an Intel i7 4770k CPU and an AMD R9 290 GPU. Testing was done at an ambient temperature of 25°C with the CPU and GPU frequencies and load changed via a combination of Unigine Heaven 4.0 and Intel XTU. As I could only monitor power draw from the wall, I used a Brand Electronics 4-1850 power meter as an indicator of system draw. Simple Kill-A-Watt units are good for basic checks, but not reliable enough for tests. At each data point, the system was left running for 30 min so that everything hit steady state before measurements were taken. Noise was measured as before, except that this was all done before disassembly and the fan was as-provided out of the box. So I was now able to plot fan RPM and noise levels vs power draw from the wall.

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There is definitely a zero RPM mode, but it does not last very long. I may have well skipped the exact point where the fan starts to spin, but even so I feel the programmed fan curve is more aggressive than necessary- especially once the fan starts to spin. In fact, the fan RPM response is taking the opposite curve to what Silverstone advertised (if it was concave as advertised, it is convex now) and this means the fan RPM increases drastically once zero RPM mode is off. That being said, it is a fairly quiet PSU owing to the fact that the fan does not spin past 50% max speed even at 50% load and is only really audible at higher wattage. Note that this unit is capable of proving well over 700 W (I tested till 800 W from the wall) and it is very likely because Silverstone decided to make this a 700 W 80+ Platinum unit as opposed to, say, an 800 W 80+ Gold unit depending on how the efficiency curve is for this platform. Either way, stick to 700 W if you can for best prolonged use.

In terms of comparison, here is how the Corsair SF600 fared (up to 700 W from the wall):

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The 120 mm fan on the SX700-LPT really comes handy here in the longer SFX-L unit, as the PSU is quieter at the same power draw levels. For example, at 400 W of power draw from the wall the Corsair SF600 is ~34 dBA loud whereas the Silverstone SX700-LPT is 30 dBA loud. No doubt the higher efficiency helps as well here, but those looking at quiet PSUs for SFF builds will do well to consider this as well.

Note that delta T (ambient/intake – exhaust) is not a very useful metric here given that the absolute temperature (or resistance) measured by the thermistor matters which is a function of ambient/intake temperatures and also system load. So this is why I am presenting the data at a fixed ambient temperature, and also take the case airflow out as a variable. Chances are the intake fan temperature in your SFF case may be higher than room ambient temperature, but that’s a case and build specific variable I can not address. To help give another set of data points, I repeated the experiment at another ambient temperature of 35 °C:

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More of the same here, except that the fan speed is increased throughout. In fact, I dare say the zero RPM mode also triggered off at <30% load here. It appears that Silverstone has just offset the fan speed higher at higher temperatures while the actual programmed fan curve vs load is the same. So the bottom line here for customers is fairly simple- try and get the fan intake temperature as low as possible. Go with a case that has low restriction dust filters for the PSU, and clean the filters regularly. If possible, have a temperature sensor near the PSU fan so you can monitor it. Do note that there is also inherent hysteresis here in that the fan will spin higher at the same load when slowing down from higher load to idle, but this is resolved fairly quickly.

A note of caution though- be it due to the zero RPM mode or the over temperature protection or a combination of both, when there are not much air flow in the hot box the PSU shut down randomly 3/10 times. Presumably the temperature read by the sensors triggered it, and so please do remember to make sure you have good airflow through your case as well. With decent airflow in the hot box, there was no such issue.

Once again, let's see how the Corsair SF600 fared:

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More of the same story here. In fact, the SX700-LPT remains in zero RPM mode a lot longer here as well in more realistic scenarios in a SFF case and having no real noise from the PSU at idle for longer is a big plus point. There is a good amount of caulk used as well to keep big components steady during transit and minimize coil whine, and I did not really notice any coil whine with this particular setup either.

Conclusion

The Silverstone SX700-LPT has an MSRP of $168 in the USA and is currently selling for $169.99 from various resellers including Newegg.com. There is no question that it is an expensive PSU considering that the closest alternative option, the Corsair SF600, can be had for $119.99. Both are relatively new PSUs, and will end up being compared against each other often as I myself did here. It is not a fair comparison, however, given that the SX700-LPT is an SFX-L unit, more efficient, uses a larger fan and gives an extra 100 W of rated power to go along with more cable options and dedicated dual 8+8 PCI-E cables for 2 high end GPUs as well. Consider this the go-to for an SFF m-ATX case then or even a full size ATX case. It is quieter than the Corsair SF600 as well, and built fairly well although I can't speak for electrical performance here. Pricing aside, my main issue here is the lackluster 3 year warranty. Is it because the fan used is not reliable enough? If so, why not use a better one? Silverstone has some good slim 120 mm fans they sell as well. Either way, the same comparison with the Corsair SF600 and its 7 year warranty will oft be made. To add to this discussion, Lian Li came out of nowhere and is selling a 750 W SFX-L 80+ Platinum rated PSU at $159.99 (albeit stock is limited at this point) which would be another potential competitor.

Overall I would definitely recommend the SX700-LPT, if only because it is tested to be a good, silent PSU and has had no issue powering a high performance, heavily overclocked rig even at a 35 °C ambient.
Silverstone SX700-LPT SFX-L PSU
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Silverstone SFX-L PSU, 700 W, 80+ Platinum Efficiency

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