When building a typical ATX gaming system, buyers have access to myriads of available power supply units (PSUs), allowing the easy selection of a product that matches their performance requirements and budget. However, the recent trend of building high performance entertainment and gaming PCs for use in the modern living room is forcing a reduction of the system’s dimensional proportions. PC case and system manufacturers are trying to compete with both each other and gaming consoles, ceaselessly introducing contemporary designs that led to the broad selection of small form factor (SFF) products available today.

Today users can easily find numerous mATX/ITX motherboards and SFF cases designed for gaming systems, but the selection of quality SFX PSU units remains very limited. A few manufacturers shyly released new SFX PSUs during the past couple of years, but still the variety of SFX PSUs is nonexistent when compared to that of normal ATX units. When trying to find SFX units capable of handling the power requirements of top-tier gaming systems, the number of available products usually can be counted on one hand.

SilverStone is a company known to invest a lot on SFF designs and has been striving to cover the needs of most users as well as possible. As far as SFX PSUs go, we have recently reviewed their mainstream ST30SF and ST45SF units, as well as the imposing SX700-LPT 700W SFX a year ago. One would think that 700 Watts are more than enough for any SFX system, but SilverStone does not seem to agree. In this review we are going to have a look at the SX800-LTI, an 80Plus Titanium certified unit with a maximum output of 800 Watts, making it the most powerful SFX PSU currently in existence.

Packaging and Bundle

We received the SX800-LTI into a large cardboard box that could fit a typical ATX unit. The box is very sturdy and we found the PSU sandwiched between thick polystyrene foam pieces inside, providing ample shipping protection. The artwork is relatively simple and mostly limited to pictures of the unit itself. 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.

SilverStone usually is not overly generous with the bundle of their products, sticking to providing only what is really necessary, and their top SFX unit is no exception to that rule. Inside the box we only found a well-written manual, a typical AC power cable and four black 3M mounting screws. Strangely, SilverStone does not supply a SFX to ATX adapter along with the SX800-LTI. They did not with the SX700-LPT either, but they do with lower output models, which is very strange, as these powerful units are far more likely to find their way into ATX-compliant cases than low-output models.

The SX800-LTI is a fully modular PSU, meaning that every cable can be detached, including the 24-pin ATX cable. Making the 24-pin ATX cable detachable usually does not make any practical sense, but it does in this case, as the user can replace the short 30 cm (11.8”) ATX cable with a longer version if the PSU is going to be installed inside an ATX case. All of the cables are “flat” type cables, with black wires and black connectors. The sole exception are the PSU-side connectors of the PCI Express power cables, which are blue.

External Appearance

In terms of specificiations, it's important to point out that the SX800-LTI is not a product that is fully compliant with the SFX specifications. As with nearly all high output SFX designs, the SX800-LTI is an “SFX-L” PSU that meets all of the SFX specifications, except from the length. It is the longest SFX unit that we have ever seen to this date, measuring 125 (W) × 63.5 (H) × 130 (D) mm (4.92" x 2.5" x 5.12"), a good 30 mm deeper than a SFX-compliant unit. This added length significantly limits the compatibility of the PSU, as a large percentage of the SFX case designs do not offer that much clearance.

Typically for a SilverStone PSU, the design of the SX800-LTI is simple, yet not aesthetically apathetic. A satin black paint with good anti-fingerprint properties covers the chassis and the company logo is subtly embossed at the top side of the PSU. Both the fan and the finger guard are black, with no lighting, but with a metallic crest featuring the company’s logo covering the fan’s engine. A dark sticker with the electrical specifications and certifications of the PSU can be found on its left side. On the right side of the chassis, which usually is out of the view of case windows, SilverStone placed the necessary white production (serial, version) and quality control stickers.

It is noteworthy to mention that SilverStone managed to fit an on/off switch next to the AC cable receptacle on the rear side of the SX800-LTI, something not very common on high power SFX designs. The front side is covered by the asymmetrically placed cable connectors. The placement of the rightmost two connectors suggests that this chassis was not initially meant to have that many connectors and that they were added by the designer after they managed to squeeze the components for an 800W behemoth in that small chassis. All of the cable connectors except from those of the ATX cable are covered with plastic protective caps.

Internal Design

A major advantage of the SFX-L chassis is that it allows for 120 mm fans to be installed, a necessity for consumer-grade products where sound pressure must be kept down to civil levels. Globe supplies the low profile 120 mm fan that we found in the SX800-LTI. It is a standard sleeve bearing model with a maximum speed of 2300 RPM at 12 Volts. Many enthusiasts will voice concerns regarding the reliability of such a high speed fan in comparison to other bearing designs, but SilverStone generally prefers to use sleeve bearing fans because of their lower noise output, even for their top-tier products. At the very least, Globe is a company with a proven high reliability record.

Most people would reasonably presume that the SX800-LTI is just a beefed-up or upgraded version of the SX700-LPT. That is not the case as the SX800-LTI is an entirely different design and is also coming from a different OEM. Enhance Electronics is behind the creation of the SX800-LTI, the OEM behind most of SilverStone’s PSUs.

The platform that the SX800-LTI is based on is not simple, yet not particularly advanced either. It is based on a proven recipe, with an LLC resonant half-bridge inversion circuit on the primary side and a typical single (12V) converter on the secondary. The minor rails are being generated via DC-to-DC converters. We have seen the same core design in computer PSUs of all efficiency ranges, including 80Plus Bronze certified units. Enhance Electronics managed to reach 80Plus Titanium efficiency levels by simply replacing the typical active electronic parts with their first-rate counterparts that have minimal energy losses. However, these ultra-high efficiency parts are many times more expensive than the typical parts we typically find in mainstream units, significantly increasing the production cost of the PSU.

Most of the filtering stage parts are behind the AC receptacle, with a few onto the main PCB. There are a total of four Y capacitors, three X capacitors, and two filtering inductors. The single rectification bridge is sharing the same large heatsink as the APFC and primary inversion side components. The passive PFC components are a large shielded filtering inductor and two 420V/270μF capacitors from Rubicon. The capacitors are the largest SilverStone could fit in there and they are practically touching the heatsink, which is worrying considering that temperature is one of the primary factors affecting the longevity of capacitors.

Despite the large heatsink housing the primary side components, there is virtually no heatsink for the secondary side conversion MOSFETs. They are mounted on the underside of the PCB and they are so efficient that the chassis of the PSU alone provides more than enough heat dissipation for them to operate seamlessly even when heavily loaded. The capacitors on the secondary side are a mix of electrolytic and solid-state products, and are coming from several different companies. We identified Rubycon, Nippon Chemi-Con, Nichicon, and Unicon capacitors in the mix. The first three companies are very well known and respected. Unicon on the other hand is not such a popular manufacturer, but they too are a Japanese-based company.

Cold Test Results

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 SilverStone SX800-LTI is surprisingly efficient, even for an 80Plus Titanium certified unit. We recorded an average efficiency across the nominal load range (20% to 100% of the unit's capacity) of 93%, with the unit maintaining a conversion efficiency above 94% when the load is between 300 and 500 Watts. The low load efficiency is relatively good but there is room for improvement, as the efficiency drops below 80% with loads lower than 40 Watts.

SilverStone designed the SX800-LTI to be semi-fanless, i.e. the fan only spins when the load or temperatures are high enough to necessitate it. 80Plus Titanium units usually work in fanless mode with a load up to several hundreds of Watts. The cooling profile of the SX800-LTI is way more aggressive than most, starting the fan when the load is higher than just 200 Watts, even when the temperatures are low. Still, that is high enough to generally ensure that the fan will never spin-up when the system is idling or performing simple tasks.

The sound pressure readings are a little higher than what we would like from a unit that is most likely going to be installed in HTPC systems, but they are not unnatural for a compact PSU with such a massive power output. Even when it fan starts spinning, the SX800-LTI maintains comfortable user levels with loads up to 550-600 Watts in room temperature. The PSU does get loud when heavily loaded, but it is highly unlikely that this PSU will ever find itself running at such loads for prolonged periods of time. 

Hot Test Results

The electrical performance of the SilverStone SX800-LTI is not greatly improved over that of the slightly older SilverStone SX700-LPT, but there is a small improvement on the output power quality. Voltage ripple figures are adequate, with our instruments recording a maximum of 36 mV, 40 mV and 32 mV on the 12V, 5V and 3.3V lines respectively. The paradox here is that the main 12V line seems to be much better filtered than the minor 5V/3.3V lines, which seem to have been somewhat neglected, perhaps because the designer just could not find enough space for more filtering components. Voltage regulation is good, with the 12V line maintaining a regulation of 2.2%. The 3.3V/5V lines are falling slightly behind, with the regulation at about 2.4%.

Although the SX800-LTI is rated for operation up to 40°C, the unit had little trouble operating inside our hotbox. Naturally, the energy conversion efficiency took a measurable hit and the average efficiency across the nominal load range dropped down to 91.6%. The reduction of the unit’s efficiency is somewhat greater at higher loads, suggesting that the active components are slightly stressed by the high ambient temperatures.

The internal temperatures of the SX800-LTI, while it was operating in our hotbox, were surprisingly low. PSUs usually reach temperatures exceeding 80°C under these operating conditions, but the SilverStone SX800-LTI hardly reached up to 75°C under maximum load. This time the cooling fan started even sooner, when a load just higher than 120 Watts. The thermal control of this unit is very aggressive, probably because SilverStone did not want to risk reducing its reliability over better acoustics performance.

Under these high temperature conditions, the cooling fan of the SX800-LTI not only starts sooner but also immediately increases its speed to audible levels. Inside the hot box, the PSU is louder with a load of just 200 Watts than with a load of 550 Watts in room temperature.  As the load increases, the speed of the fan constantly increases as well, reaching its maximum possible speed when the load exceeds 700 Watts. Thankfully our hotbox test is one of extremes and that - outside of poorly ventilated cabinets - few home users have environments this warm, as the sound pressure levels with a load above 500 Watts under these conditions would be practically intolerable for home users. 

Conclusion

ATX PSUs were the focus of R&D for decades while, at the same time, SFX designs were hardly available at all. This led to a massive performance gap between ATX and SFX units, as the latter started appealing to home users and gamers just a few years ago. Only a couple of years ago, the power quality of SFX units still was rather poor. The SilverStone SX700-LPT and, later on, the Enermax Revolution SFX 650W were the first SFX units that gave us performance figures on par with high-performance ATX units.

SilverStone is a company strongly focused on the R&D of small form factor cases (SFF), systems, and other related parts. They have several compact cases and products designed for high-end living room systems, including designs that were designed with gamers in mind. Therefore, their efforts to market the very best SFX PSUs available are not unfounded.

The SX800-LTI not only brings a record-high power output for an SFX-L design, but also is even further improved, with exceptional energy conversion efficiency and better power output quality than its predecessors. Note that the power quality is still not on par with that of top-tier ATX PSUs and it definitely is much louder than any equally powerful ATX design, but it would unquestionably be unfair to compare the SX800-LTI to any ATX unit. As far as SFX/SFX-L designs go, the SX800-LTI has the best overall performance that we have encountered to this date.

The extra length of the SX800-LTI makes it incompatible with most SFX-compliant cases. According to their compatibility charts, even most of SilverStone’s own cases are incompatible with this PSU. Its short wires make it incompatible with ATX-compliant cases as well, plus there really is no reason to purchase such an expensive SFX-L unit if one is planning to use an ATX-compliant case, as ATX PSUs are significantly less expensive and there is a much wider selection available. That the SX800-LTI is fully modular and there are adapters/cable sets available to allow its installation in an ATX case is a boon, but only for those that, for any given reason, may have to switch from their SFX-based system to an ATX-based system in the future.

The only real problem with this unit is that it lacks purpose. The SX800-LTI has only one CPU/EPS 8-pin connector, meaning that it cannot be used to power top-tier motherboards that have two 8-pin connectors, which is reasonable considering that current designs of such motherboards are all but impossible to fit inside SFX-compliant cases anyway. That leaves only the GPU(s) as the major load of the system. The power output and class of the SX800-LTI suggest that it needs at least two GPUs to even reach efficient loading levels. The only configuration that could bring the PSU’s loading up to 50-55% is that of SilverStone’s only compatible case, the RVZ02/ML08, with an NVIDIA TITAN V or AMD VEGA 64 installed. When moving to Micro-ATX motherboards with two PCIe ×16 slots, such as the Asus ROG Strix Z270G, cases that are roomy enough to house two full-size graphics cards also support ATX PSUs, so the SX800-LTI is an unappealing option. Only a SFX-compliant case designed for high-end Micro ATX motherboards is the natural habitat of the SX800-LTI, and there just are not many (if any) available at this time.