The SilverStone SX700-LPT SFX 700W PSU Review

As PC gaming continues to grow, more and more PCs are finding their way into the living room. As such, the demand for small, elegant computers that are powerful enough to be used as gaming machines is constantly on the rise. Several reputable manufacturers have presented products specifically designed for living room PC gaming, from subtle gaming cases to specialized keyboards/mice.

One major challenge with developing these small form factor (SFF) gaming systems is power. A gaming PC can require a lot of power, which can be an issue with cases that only support SFX PSUs. As the market for SFX units is very low and such systems were not expected to have high power requirements to begin with, there are very few designs available with a power output higher than 500 Watts.

SilverStone is a company that is strongly focused on the design and development of SFF cases, with several of their recent products designed to be used primarily as gaming machines. They are one of the very few companies that offer advanced, high performance SFX PSUs. In this review we are having a look at the SX700-LPT, their latest and greatest SFX PSU design. The SX700-LPT is 80Plus Platinum certified and has a maximum power output of 700 Watts, theoretically making it the most advanced consumer SFX PSU available today.

SilverStone supplies the SX700-LPT SFX PSU into a relatively large cardboard box for an SFX PSU. The box is very sturdy and the PSU is sandwiched between thick polystyrene foam pieces, providing ample shipping protection. The most basic features of the PSU can be read at the front side of the box and more details are printed on the back.

The bundle of the SX700-LPT is spartan, with the company supplying only a manual, an AC power cable and four black mounting screws. The manual is extensive and detailed. SilverStone does not provide a SFX to ATX adapter with the SX700-LPT, which is peculiar considering that they do with less powerful units.

This is a fully modular design so every cable can be detached, including the 24-pin ATX cable. All of the cables are “flat”, ribbon-like, including the thick 24-pin ATX cable. Apparently, SilverStone is trying to save as much space as possible. Be warned that these cables are much shorter than those of a regular ATX unit, with the ATX power cable being just 30 cm (11.8″) long. Every cable is made by using black wires and black connectors, with the sole exception of the PSU-side connectors of the PCI Express power cables, which are blue.

While the SX700-LPT obviously is very small compared to an ATX PSU, it does not actually adhere to SFX specifications either. It is being labeled as an “SFX-L” design, with its chassis measuring 125 × 63.5 × 125 mm (W×H×D). Essentially, it is 25 mm longer than a standard SFX PSU. The longer chassis allowed SilverStone to fit more components and a 120 mm cooling fan, but it could very easily cause compatibility issues with some cases that do not have any extra space behind the PSU.

The chassis is sprayed with a satin black paint that is fingerprint resistant. Oddly, SilverStone punched their company logo along the top side and placed the sticker with the electrical specifications and certifications on the left side of the chassis. It is likely that the company expects the top of the PSU to be more frequently visible than its side, but such aesthetic improvements are of questionable value on such products, as cases that require SFX PSUs rarely have windowed panels anyway.

The rear of the SX700-LPT is somewhat interesting in its own way. There is only an AC cable receptacle and an on/off switch, yet such a switch is relatively rare on SFX designs. The connectors for the modular cables can the seen at the front side of the unit, with the PCI Express cable connectors being blue and every other connector being black.

Zhen Poweryear is the supplier of the thin 120 mm fan found inside the SX700-LPT. It has a black frame but semi-transparent tinted blades. We could not find specific information on the PY-12015H12S, but it appears to be a sleeve bearing engine fan and has a maximum speed of about 1700 RPM.

Most of SilverStone’s SFX PSU designs come from Enhance, but this is not the case with the SX700-LPT, which is a Sirfa design. Naturally, everything is very densely packed due to the limited space, but the design is actually very clean for a high power SFX unit. The filtering stage begins at the back of the AC receptacle and continues on the main PCB, with four Y capacitors, three X capacitors and two filtering inductors in total.

The heatsink at the far right side of the PCB holds the active PFC components, two transistors and a diode. Rubycon supplies the PFC 420V/390μF capacitor. The main inversion stage is a half-bridge configuration with two MOSFETS, which are found on the heatsink near the center of the design. The secondary side conversion MOSFETs are at the underside of the PCB, while DC to DC conversion circuits can be seen on the vertical daughterboards. Nippon Chemi-Con supplies all of the secondary capacitors, electrolytic and solid-state alike.

For the testing of PSUs, we are using high precision electronic loads with a maximum power draw of 2700 Watts, a Rigol DS5042M  40 MHz oscilloscope, an Extech 380803 power analyzer, two high precision UNI-T UT-325 digital thermometers, an Extech HD600 SPL meter, a self-designed hotbox and various other bits and parts. For a thorough explanation of our testing methodology and more details on our equipment, please refer to our How We Test PSUs – 2014 Pipeline post.

The efficiency of the SilverStone SX700-LPT is excellent, meeting and surpassing the 80Plus Platinum guideline with an input voltage of 230V AC. Our instruments measured a maximum efficiency of 94.3% at 50% load and an average efficiency across the entire nominal load range (20% to 100% of the unit’s capacity) of 92.5%. The low load efficiency of the PSU is outstanding as well, with a reading of 89.2% and 81.4% under 10% load and 5% load respectively.

The SX700-LPT sports a semi-fanless design, meaning that the fan will start only after the load is higher than 150W. Due to its densely packed design, the internal temperatures of the SX700-LPT rise sharply until the fan starts, but the internal temperatures drop down to reasonable levels once the fan is working. When operating in room temperature, the cooling fan is relatively tolerable with loads only up to 500 Watts. Beyond that point, the thin fan speeds up significantly in order to keep up with the cooling needs of the PSU, reaching above 44 dB(A) at maximum load, an uncomfortable noise level for casual use.

We do not usually have great expectations regarding the power output quality of SFX PSUs, as the few we have reviewed to this date displayed poor power quality figures. The SX700-LPT pleasantly surprised us by delivering both good voltage regulation and ripple suppression. Voltage regulation on the 3.3V/5V lines is at about 2.5% and the 12V line is even stronger, maintaining a regulation of 2% within the nominal load range. Filtering is good as well, with our instruments recording a maximum voltage ripple of 52 mV on the 12V line. The 3.3V and 5V lines both recorded a maximum ripple of 24 mV, for a design limit of 50 mV.

Although we performed our first cross-loading test without any issues, we could not complete the second cross-loading test that is meant to test the 3.3V and 5V rails – or any test with a load below 200 Watts for that matter. The reason is simple: the fan of the SX700-LPT is programmed to start only at loads above 150 Watts, regardless of the ambient temperature. We could not maintain operating temperatures with a load between 120 and 150 Watts inside our hotbox, the PSU was shutting down to protect itself. Therefore, we only performed tests with a load greater than 200 Watts.

We need to stress that this is a PSU rated at 40°C and we perform our testing at temperatures higher than 45°C – we could reduce the ambient temperature of our hotbox testing but we chose not to do so as the results would then not be comparable to those of our previous reviews.

The energy conversion efficiency of the SX700-LPT takes a significant drop inside our hotbox, especially under heavy loads, indicating that the internal temperatures of the PSU are uncomfortably high. The average efficiency reduction is 1.4%, with a high drop of 2.1% at 100% load. The active parts of the PSU are good and such an efficiency loss cannot be attributed solely to them, as they have to cope with very high internal temperatures that reduce the efficiency of even the best of parts.

As we started testing the PSU with a load of 210…