One of the many great outcomes of the general push towards small form factor (SFF) systems is that it has encouraged hardware developers to rethink size across all of their products. Does a video card really need to be longer than a sub sandwich? Does a laptop need to be two inches thick? Does a computer case need to be two feet tall? Sometimes the answer to those questions is still yes; but in other cases it turns out there's room for improvement – or rather, there is room to trim. And, as we're going to see today, this applies to power supplies as well.

SilverStone is a company known for their interest on the development and marketing of small system components, with their R&D department continuously releasing unique case designs and high-performance parts designed with reduced dimensions in mind. The company is also very active in the power supply unit (PSU) market, with a long track record and currently offering dozens of products. Their engineers are very experienced on the design and development of advanced PSUs, continuously setting new milestones, such as with the recent release of the 800W and 1000W SFX-L designs.

So perhaps it's only fitting that SilverStone has introduced one of the first 1200W power supplies that is actually ATX-compliant, in the form of the Strider Platinum ST1200-PTS.

Now, to be sure, there are plenty of 1200W power supplies on the market. However, technically none of these PSUs actually comply with the base ATX standard. ATX, the heart of the desktop computer as we know it, officially calls for power supplies to be 140mm in length. For practical purposes that requirement is frequently ignored in high-end builds – high-power PSUs have needed more space, and big cases have made sure to give them just that – but it none the less has a limiting effect on just what options are available for building a high-power system. Until recently, you couldn't have a high-capacity PSU in a case that didn't go beyond the ATX specifications.

SilverStone, with their Strider Platinum ST1200-PTS, is looking to change that. The latest addition to the company's PSU designs, it is the upgrade of the Platinum ST1200-PT that we received and reviewed last year. For the S(mall) version of the PSU, the company’s engineers have reduced the length of the chassis by an astounding 40 mm – bringing it down to 140mm in length – allowing the 1200W PSU to fit into any ATX-compliant case.

Packaging and Bundle

The new Strider Platinum ST1200-PTS PSU comes in an aesthetically simple but very functional cardboard box that is small enough to hint the dimensions of the included unit. It is a very sturdy box and additional foam layers provide excellent shipping protection. There are plenty of technical details and information printed on all sides of the box.

Inside the box we found a relatively rich bundle, consisting of a detailed user's manual, a thick AC power cable, black cable ties, a few short cable straps, a set of black mounting screws, a set of black thumbscrews, and a magnetic nylon fan filter. The fan filter is meant to protect the PSU from dust but it can be placed anywhere on the case if the PSU's compartment already features a filter.

SilverStone is using flat "ribbon" type cables, made using all black wires and connectors. This includes the ATX cable and the CPU/PCI-E 12V connectors. The only exception at the blue connectors at the PSU side of the PCI Express power cables. The ATX cable is made of several smaller ribbons bundled and secured together, forming a sort-of round cable.  

External Appearance

A mere glance at the SilverStone ST1200-PTS is enough to puzzle experienced eyes. Many cautious experts may even doubt that a true 1200 Watt PSU can fit into a standard ATX chassis when manufacturers had trouble fitting half that power output into the same dimensions not too long ago. Nonetheless, it is a fact that SilverStone managed to fit the components into a chassis that is merely 140 mm long, which is shorter than the average 600-700 Watt PSUs that we commonly review. The dimensions of the ST1200-PTS comply fully with the ATX standard, meaning that it will fit in any case designed to hold an ATX PSU.

The chassis of the ST1200-PTS is sprayed with textured black paint. It is a bit coarse but also smudge and scratch-resistant. The sticker with the PSU's electrical specifications covers the entirety of the chassis’ left side, while the right side is almost completely plain, with just small version and serial number stickers present. A metallic badge with the company's logo covers the center of the 120 mm cooling fan.

Naturally, the front side of the ST1200-PTS is almost completely covered by the connectors for the modular cables. SilverStone placed plastic caps on some of the connectors but more than half of them are uncovered. The CPU and PCIe do not share the same connectors, with the former being blue and the latter black. These connectors look the same but they are keyed so, for example, the PCIe cables will not fit in the CPU connectors. The rear of the PSUs is a bit interesting – although there is only a standard AC cable receptacle and a small on/off switch, it is interesting to see that the designer did not remove the switch in order to save space, a common technique for engineers designing compact ATX/SFX PSUs.

Internal Design

The fan responsible for the cooling of the ST1200-PTS is a Yate Loon D12SH-12. It features a relatively simple rifled sleeve bearing engine and has a very high maximum rotational speed of 2200 RPM. We did not expect to find such a simple fan inside such a high-end product, but on the other hand, this fan series is proven to be very reliable. So perhaps it is not too strange that SilverStone opted to trust the cooling of the ST1200-PTS to this particular fan.

SilverStone entrusted the creation of the ST1200-PTS to Enhance, the OEM that usually is behind SilverStone’s advanced PSUs. The platform seems to be a shortened version of the design that Enhance has been working on for many years and that the ST1200-PT was based on. The designer managed to reduce the dimensions of the original design mainly by reducing the dimensions of the input/APFC circuitry and by improving the efficiency of the original platform, effectively reducing the unit’s cooling requirements.

The filtering stage of the PSU is adequate, with four Y capacitors, three X capacitors and two filtering inductors. Some parts are left floating next to the AC receptacle, trapped next to the cooling fan, with practically zero mechanical support. The other components are all very well secured, with perhaps a bit excessive use of thermal glue by the assembly line. Two very large Nippon Chemi-Con 450V/560μF capacitors are taking up most of the space next to the APFC circuitry heatsink.

The primary inversion circuit consists of four MOSFETs that form a LLC resonant full-bridge converter design. A single 12V line is generated at the secondary side of the PSUs by a rectifier configuration formed by eight high efficiency MOSFETs. The minor 3.3V/5V lines are generated via DC-to-DC converters, which can be seen on their own small PCBs. The filtering capacitors are a mix of electrolytic capacitors from Nippon Chemi-Con and solid-state capacitors from several manufacturers, such as Nippon Chemi-Con and Unicon.

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 energy conversion efficiency of the SilverStone ST1200-PTS at room temperature is just sufficient enough to justify the unit’s 80Plus efficiency certification. It meets the 80Plus Platinum certification requirements for an input voltage of 115 VAC, reaching up to 92.1% efficiency at 50% load and holding an average nominal load (20%-100%) efficiency of 90.7%. In our testing the PSU cannot meet the 80Plus Platinum efficiency certification requirements for an input voltage of 230 VAC, failing to reach 94% efficiency at 50% load, yet the average nominal load (20%-100%) efficiency of 91.6% is good.

The thermal control circuitry of the SilverStone ST1200-PTS is simple, meaning that there is no “fanless mode” or some other advanced control method, with the circuitry simply controlling the speed of the cooling fan depending on the temperature and load of the PSU. We found the control algorithm a little peculiar, as it holds the speed of the fan at very low levels while the load is lower than 450 Watts but then increases the speed of the fan almost exponentially, reaching its maximum speed within a range of just a few hundred Watts. This effectively makes the ST1200-PTS very quiet at loads below 450 Watts and very loud at loads above 650 Watts.

Hot Test Results

Enhance is not an OEM who is known to focus on top-tier power quality delivery, and the tight dimensions of the ST1200-PTS certainly did not help the designer to improve much on that. The maximum voltage ripple on the 12V line reaches 86 mV under full load, quite close to the recommended design limit. The same stands for the 3.3V line, the voltage ripple of which reaches 42 mV under full load, with the 5V line faring a bit better. Severely cross-loading the PSU will cause the ripple to increase even further but the figures still stay within the recommended design limits. Voltage regulation on the other hand is exceptional, with the ST1200-PTS holding the 12V line at just 0.8% across the load range, with even tighter regulation on the 3.3V/5V lines.

The SilverStone ST1200-PTS is rated at 40 °C, meaning that the manufacturer specifies that it can output its advertised power when the ambient temperature is at or lower than 40 °C. Efficiency testing takes place at 25 °C and it degrades as the temperature increases, meaning that most units will not meet their certification requirements while we are testing them into our hot box. This is true for the ST1200-PTS, the efficiency of which drops by an average of 0.5% while operating into our hotbox and slightly below the 80Plus Platinum certification limits. On the other hand, the unit did reach its maximum 1200 Watts power output with an ambient temperature of 48 °C without issues, indicating fair resistance to thermal stress.

High ambient temperatures trigger the thermal control circuit to push the fan at its maximum speed very quickly. Although the PSU still is relatively quiet at very low loads, the fan’s speed goes to the maximum at 50% load, shooting the noise level of the ST1200-PTS to uncomfortable figures. Nevertheless, the internal temperatures of the PSU are, considering the very high output and the small volume of the unit, very low, ensuring the longevity of the unit. Thermal degradation is rather severe at very high loads and efficiency figures plummet, which is expected from such a design that is being pushed well above its rated temperature specifications – that it managed to output its full rated output is quite the feat as it is.

Conclusion

SilverStone’s engineers designed the ST1200-PTS to appease a very specific market – builders who need a high-wattage power supply in a confined space. As a result, the ST1200-PTS is the only 1200W PSU that we know of that has a fully ATX compliant, 140 mm deep chassis. Although this may not be important for power users who often use large tower cases, it is of utmost importance to builders who are trying to assemble very powerful systems into very small ATX cases, such as top-tier living room gaming systems.

Dissecting the ST1200-PTS from an engineering standpoint, trying to fit more components into a smaller space is very possible – as we've seen first-hand – but not without some trade-offs. Components have become smaller and more efficient as technology advances, allowing engineers to build shorter and more powerful PSUs, however we're not yet at a point where it's possible to have such a powerful ATX-compliant PSU with all the bells and whistles installed into it, while still remaining cost-effective. As such, the ST1200-PTS is a relatively simple PSU, without fancy features – aesthetic or otherwise. Thankfully, the compromises that SilverStone had to make are not severe. The most apparent compromise from a user’s point of view is the simple cooling circuitry, with a standard 120 mm fan handling the thermal needs of the unit. A deeper analysis reveals less complex filtering circuitry, which is the cause of the unit’s relatively high voltage ripple figures.

The overall performance of the ST1200-PTS is acceptable. Although it definitely is no match for many other top-tier units of similar power output, it does not fall outside of the ATX design recommendations either. Power quality figures are passable – although the voltage ripple flirts with the design limit on the 3.3V and 12V lines when the unit is under maximum load, it never surpasses that limit regardless of the operating conditions, and the regulation of the voltage lines is excellent.

Despite the compact dimensions of the unit and the use of a 120 mm fan, internal temperatures are low and thermal degradation is very limited. The only truly negative performance aspect that we must address is the very high noise when the unit is heavily loaded, which will not bother gamers who use headphones or loud speakers but it would certainly be a problem for users that want or need a relatively quiet environment. Note that the ST1200-PTS is noisy only when it is heavily loaded, as there is not a single (rational) PC configuration that is going to have a power draw greater than 300 Watts while the system is idling.

Overall, we feel that SilverStone will have trouble competing against typical top tier >1 kW alternatives, as their performance generally is superior over one or more aspects. When the length of the PSU is not very limited, there are competitive products which are both cheaper and better performers. On the other hand, the ST1200-PTS is the only option for users who are limited to fully ATX compliant units and cannot use a PSU longer than 140 mm. If that is the case, then the ST1200-PTS is a power supply that will not disappoint as the heart of a powerful modern gaming system.