As high-performance entertainment and gaming PCs are gaining ground, manufacturers are placing greater effort on the development of better and more efficient small form factor (SFF) parts. These days it's possible to build an advanced gaming PC that rivals gaming consoles in terms of size, at least so long as you have an appropriate SFX power supply unit (PSU) capable of delivering enough current to a power-hungry graphics card.

Not more than a few years ago, it would have been very difficult (and costly) to purchase a high performance SFX PSU. As the market demand for such units increased, some companies jumped on the opportunity and added a couple of SFX units into their product lineups. Although their overall performance was much better than the average run-of-the-mill SFX PSU, their cost was relatively high and their performance was not quite comparable to that of regular ATX units, especially when it came to acoustics. The market matured quickly though and this year we are seeing a number of new SFX PSU platforms appearing, promising performance comparative to that of advanced ATX units.

Corsair is one of the first companies that released advanced SFX PSUs into the market. Their SF PSU series used to be one of the very few choices that advanced users had when building a system requiring an SFX PSU. Corsair usually upgrades their PSUs without renaming them or their series, and this month the company decided to give their SF series a revamp. The new SF series units now come with an 80Plus Platinum efficiency certification and very impressive electrical specifications.

In this review we are having a look at the SF450, the less powerful model of the series that has a maximum power output of 450 Watts. The SF450 has an MSRP price of $99 and seemingly is a quite cost-effective solution for an advanced PSU powering a single graphics card SFX gaming system.

Packaging and Bundle

We received the SF450 in a medium-sized cardboard box with the same yellow/black artwork that the company has us used to over the past several years. The artwork is simple and clean, with the front focusing on a subtle picture of the unit itself and the detailed information moved to the rear and sides of the box. Inside the box, we find the unit well packed, protected between foam paddings and inside a reusable nylon pouch.

The bundle of the SF450 is relatively rich for a PSU. Corsair supplies the typical AC power cable, black 3M mounting screws, a very thorough multilingual manual, a case badge, a few short cable ties, and a couple of cable straps. The company also supplies an SFX to ATX case adapter that will certainly be useful to users who upgrade or fiddle with their systems often.

The new SF450 SFX PSU is fully modular. Its stock cables are a little shorter that those of a standard ATX PSU, which may cause compatibility problems when trying to install the unit inside a large ATX case. Corsair does offer longer cable versions but at an additional cost. All of the connectors and cables are black, with individually sleeved wires. This creates a unique aesthetic effect and does not make the cables as stiff as we thought they would be. Flat ribbon-like cables would probably be a little better for very tight spaces, as they are more flexible and take up less space.

The Corsair SF450 450W SFX PSU

External Appearance

Corsair’s latest upgrade of the SF series perfectly matches the size requirements of the SFX standards, measuring 125 × 63.5 × 100 mm / 4.92 × 2.5 × 3.94 in (W×L×D). Its chassis is sprayed with a matte black paint that is slightly resistant to fingermarks. The size of the chassis limited the designer to using a 92 mm fan, the grey blades of which create a subtle visual antithesis with the matte black chassis and glossy black finger guard.

Corsair placed a decorative sticker on the left side of the chassis, where it will be visible from a windowed side panel. We also found the company logo engraved in between a parallel rib pattern at the top side of the chassis, probably because the designer expects users to install this PSU with its fan facing downwards (assuming a “classic” tower case with a windowed left side panel). The sticker with the electrical specifications and certifications of the unit is on the right side of the chassis.

On the rear side of the Corsair SF450 PSU we can see an AC cable receptacle, a small switch, and a small label with the unit’s model number. The front side hosts the connectors for the modular cables and a very basic legend. Different cables use different connectors and cannot be mismatched. Note that PCIe and CPU 12V cables are using the same connectors on the PSU’s side.

Internal Design

The 92 mm fan taking care of this PSU’s cooling needs is actually the same NR092L low-profile fan that Corsair has been using with the previous version of the series. According to its identification number, Corsair appears as the manufacturer of the fan, so haven't been able to determine who the OEM behind its creation really is. What we do know is that it has a rifle bearing engine and a maximum speed of 3950 RPM. Running anywhere near that speed would make the small 92 mm fan very loud but, as we will see in the following pages, the high efficiency of the PSU allows it to keep the fan’s speed low under normal operating conditions.

The OEM behind the new Corsair SF450 is none other than Great Wall, the Chinese company that nowadays is behind several high-performance designs. The platform appears to be the same as the one Corsair used for the original SF series, which were granted the 80Plus Gold efficiency certification. We do not have one of the older units at our disposal for a thorough comparison but, comparing it to the reference design images, it appears that Great Wall achieved the higher efficiency certification level by simply using newer and more efficient active components. If there are any layout/design changes, these should be minor.

The filtering stage begins on the tiny PCB at the back of the AC receptacle and continues onto the main PCB, with a total of four Y capacitors, two X capacitors, and three filtering inductors. A very simple, straight heatsink holds the single rectification bridge, as well as the APFC and primary inversion circuit active components. The APFC circuitry consists of a single transistor and a diode that are paired with a comparatively very large coil and capacitor. The bulky 420V/390μF capacitor is supplied by Nippon Chemi-Con and is perhaps a bit too large for a 450W PSU.

Despite the high efficiency certification of the Corsair SF450 PSU, the circuitry actually is relatively simple. The heart of the primary inversion stage are two MOSFETs that form a standard half-bridge LLC inverter. Four MOSFETs at the secondary side of the transformer generate the 12V line of the PSU and two DC-to-DC circuits on the vertical daughterboard generate the nowadays secondary 5V/3.3V lines. All of the secondary side capacitors, electrolytic and polymer alike, are supplied by Nippon Chemi-Con as well.

Cold Test Results

For our PSU testing, we are using various 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 new SF450 does meet the 80Plus Platinum certification standards when powered from a 110V AC source. In this case, the nominal load range (20% to 100% of the unit's capacity) efficiency is 91.2%. It does not meet the 80Plus Platinum 94% efficiency limit at half load when the input voltage is 230V, with our equipment reading an energy conversion efficiency of 93.8%, yet the nominal load range efficiency is once again very high, at 92.8%. The Corsair SF450 also appear to be very efficient when handling low loads, with the conversion efficiency staying above 80% when the PSU is powering a load of just 22.5 Watts (5% capacity).

Despite its compact dimensions and relatively small cooling fan, the thermal performance of the Corsair SF450 is excellent. The thermal regulation circuitry is perhaps a little too aggressive, as the fan starts when the unit is barely warm. Our temperature readings were surprisingly low even when the unit was operating at 100% capacity, even for an 80Plus Platinum certified unit.

Unlike what someone would expect from an SFX PSU that maintains very low operating temperatures, the Corsair SF450 is surprisingly quiet as well. A load of less than 100 Watts is enough to start the fan but the sound pressure level remains very low across the entire load range. The noise coming from the SF450 should be noticeable only when the load is higher than 350 Watts and never reaches levels that we consider uncomfortable for any kind of user.

Hot Test Results

Earlier SFX PSU designs were notorious for their poor power quality figures. More recent models, like the SilverStone SX700-LPT and the Enermax Revolution SFX 650W, were greatly improved. The Corsair SF450 places the standards even higher, delivering electrical performance that most ATX units would be envious of. The 12V voltage line regulation is at 0.4%, an exceptional figure, which goes up to about 1.3% for the less strictly controlled 3.3V and 5V lines. Line filtering is excellent too, with our instruments recording a maximum of 26 mV, 14 mV and 12 mV on the 12V, 5V and 3.3V lines respectively. These figures hardly change even when the PSU is heavily cross-loaded, which is to be expected from a modern platform.

The Corsair SF450 managed to retain most of its energy conversion efficiency while it was operating inside our hotbox. Despite the adverse operating conditions, the average efficiency drop was less than 1% and evenly distributed across the entire load range, suggesting that the components are handling these adverse conditions very well, with no signs of thermal stress.

The small 92 mm cooling fan handled the cooling needs of the SF450 much better than what we expected it would. Even though the ambient temperature is very high and the fan starts with a load of just forty Watts, the noise output remains at comfortable levels until the load exceeds 250 Watts.

After that point, the speed of the fan will increase at a significantly greater rate and the SF450 does become loud when heavily loaded inside our hotbox. These are not regular operating conditions and yet the Corsair SF450 shows that it can maintain trouble-free operating characteristics, even if at the expense of its acoustics performance.

Conclusion

Even though the demand for high performance SFX PSUs is on the rise, few companies actually allocate their R&D resources to improving their SFX units. Corsair is one of the rare examples of a company that released a very successful SFX PSU series and, instead of sitting on their laurels, redesigned those PSUs to improve their efficiency rating and overall performance without notably raising the retail cost. The SF450 version that we reviewed today is capable of powering the majority of gaming PCs, which comprise of a good CPU and a single high-performance graphics card.

Great Wall, the OEM behind the creation of the SF series, may be a relatively new company when it comes to high performance PC designs, yet the company repeatedly proved that they can deliver excellent products. Corsair’s engineers did a great job improving both the reliability and the performance of the platform, resulting to a new PSU that is more efficient, runs cooler, and performs better. Although the new 80Plus Platinum certified SF series is technologically rather simple, the platform is very efficient. Most of that efficiency comes from the very high-quality active components. These components also have very low thermal losses and a wide operating range, allowing the SF450 to remain very efficient regardless of the load and greatly improve the PSU’s longevity and overall performance. The passive components are of excellent quality as well, coming from reputable manufacturers.

In terms of performance, the SF450 pleasantly surprised us on just about everything. The electrical performance of the unit is exceptional, with line filtering and regulation that rivals most of the top-tier PSU platforms. The conversion efficiency initially seems barely good enough, honoring its 80Plus Platinum certification only when powered from a 115V AC source, but it is the extraordinary low-load efficiency that really stands out here, as well as the unit’s resistance to thermal stress. Finally, despite the use of a thin 92 mm cooling fan, the thermal performance of the SF450 is excellent and, on top of that, the noise output of the PSU is very low. It is unlikely that the noise coming from the SF450 will ever reach bothersome levels while the PSU is powering a typical gaming system, even if installed in a poorly ventilated environment.

With its high overall performance and considering its power delivery capabilities, the SF450 is the ideal choice for typical SFF living room gaming systems. The MSRP price of $99 seems a little high for a 450W PSU but, considering that retail prices tend to be significantly lower and the current price trends of SFX PSUs, it is not unreasonable. We believe that the new SF series will become a favorite amongst users who build high performance SFF systems.