When looking at the Seasonic Power Supply test results we see two values, wattage and volt-amps. Since it might not be clear what they measure, here's a brief overview.

The volt-amp (VA) value is how much real power is being consumed by the power supply being tested to provide the wattage (W) value. The higher the VA value is, the more electricity is being used by the power supply. Because no electrical device is 100% efficient, there will always be some loss when converting AC to DC. The closer the Volt-Amps (VA) and Wattage (W) figures are, the more efficient a power supply is. This is called the Power Factor: Watts / Volt-Amps = PF.

Since we're testing with a 120W dummy load, the load on the power supply (wattage) should be as close to this figure as possible. Anything above this load in apparent power describes the overhead and wasted energy (given off as heat) for the particular power supply being tested. For the unloaded tests, the wattage and volt-amp figures should be as close as possible to one another. The lower the figures are, the less power is being wasted.Measurements were taken with an Extech 380803 Power Analyzer.

Seasonic Power Load Tests Power Supply Model Wattage Test Type Loaded Unloaded Seasonic SuperTornado 400 W (A-PFC) Active Power 177 W 6 W Apparent Power 182 VA 7 VA Vantec iON2 350 W Active Power 192 W 10 W Apparent Power 277 VA 21 VA Antec TruePower 330 330 W Active Power 195 W 22 W Apparent Power 289 VA 38 VA Ultra X-Connect Green UV 500W 500 W Active Power 193W 22 W Apparent Power 307 VA 40 VA AOpen Silent Power AO400-12AHN 400 W Active Power 179W 9 W Apparent Power 275 VA 18 VA Seasonic S12-430 430 W (A-PFC) Active Power 179W 6W Apparent Power 180VA 9VA PC Power and Cooling Turbo-Cool 510 Express/SLI 510 W (A-PFC) Active Power 200 W 29 W Apparent Power 202 VA 32 VA HEC Ace Power 580UB 580 W Active Power 183 W 12 W Apparent Power 272 VA 26 VA HEC Win 550UB 550 W Active Power 184W 10W Apparent Power 263VA 22VA Akasa PowerPlus AK-P550FF 550 W (A-PFC) Active Power 194W 38W Apparent Power 197VA 40VA AOpen Prima Power AO700-12ALN 700 W (A-PFC) Active Power 172W 3W Apparent Power 181VA 9VA PC Power & Cooling Turbo-Cool 1KW 1000 W (A-PFC) Active Power 205W 25W Apparent Power 207VA 32VA Seasonic S12 600 600 W (A-PFC) Active Power 164W 7W Apparent Power 173VA 9VA Mushkin Enhanced XP-650 650 W Active Power 192W 22W Apparent Power 279VA 43VA Seasonic S12 Energy Plus SS-650HT 650 W (A-PFC) Active Power 150W 7W Apparent Power 150VA 10VA Seasonic M12 700W 700 W (A-PFC) Active Power 161W 8W Apparent Power 165VA 11VA Corsair HX620W 620 W (A-PFC) Active Power 171W 8W Apparent Power 173VA 12VA Zalman ZM600-HP 600 W (A-PFC) Active Power 173W 5W Apparent Power 175VA 9VA HEC Zephyr 650 650 W (A-PFC) Active Power 185W 12W Apparent Power 190VA 17VA GlacialPower GP-PS550BP 550 W Active Power 178W 6W Apparent Power 269VA 17VA Cooler Master Real Power Pro 750W 750 W (A-PFC) Active Power 158W 6W Apparent Power 163VA 9VA Cooler Master Real Power Pro 750W 750 W (A-PFC) Active Power 158W 6W Apparent Power 163VA 9VA Seasonic S12 II 500W 500W (A-PFC) Active Power 145W 7W Apparent Power 148VA 10VA Enermax Infiniti 720W 720W (A-PFC) Active Power 179 W 12 W Apparent Power 181 VA 18 VA COOLMAX GREEN POWER CUQ-1200B 1200W (A-PFC) Active Power 172 W 9 W Apparent Power 193 VA 12 VA PC Power & Cooling Silencer 750 Quad 750 (A-PFC) Active Power 168 W 12 W Apparent Power 175 VA 15 VA Enermax Galaxy EGX850EWL 850 W (A-PFC) Active Power 184 W 11 W Apparent Power 193 VA 16 VA Seasonic M12D 750 750W (A-PFC) Active Power 169W 7W Apparent Power 173VA 9VA Seasonic S12D 850 850W (A-PFC) Active Power 148W 7W Apparent Power 149VA 10VA Seasonic X-750 750W (A-PFC) Active Power 139W 6W Apparent Power 141VA 8VA Seasonic X-460 (SS-460FL) 460W (A-PFC F3) Active Power 162W 10W Apparent Power 164VA 14VA Seasonic X-760 (SS-760KM) 760W (A-PFC F3) Active Power 161W 6W Apparent Power 164VA 10VA

The Seasonic X-460 power supply uses 162W of power when a 120W power load is hooked up, which is 74% efficiency at 26% load of its rated 460W power output. The Seasonic X-460 Fanless is rated for 88.18% efficiency at 20% load according to 80Plus specs, so the results we're seeing here are apparently a bit off from the 80 Plus Gold certification. Power factor is 0.98PF.

Unloaded power draw is about 10W, or 14VA for a power factor of 0.75PF.

The 460W Seasonic X-460 Fanless is an interesting power supply for a niche section of DIY computer builders. Used in an appropriately ventilated computer case it opens up a world of quieter home theatre PCs, or perhaps laboratory or recording studio environments where noise from traditional power supply fans is unwanted. At 460W, the X-460 is well sized for the power demands of mainstream computer systems built around motherboards or processors with integrated graphics, although it does include two PCI Express auxiliary power connectors for discrete videocards.

The computer case is the key variable in the silent computer equation, it's also the hardest for us to comment or give guidance on.

The reliance on convective cooling means the Seasonic X-460 Fanless power supply is not suitable for all environments. A climate controlled office is likely fine, a hot un-airconditioned New York apartment in the middle of a summer heat wave.... likely not. Similarly, a computer case without any vents above the power supply, or worse where the top of the power supply butts up against the metal panels is simply not going to work here.

Seasonic are pretty vague on what constitutes a "well designed system chassis," so a certain amount of common sense from the user is required. Ensure the case has good ventilation above the power supply and sufficient cool air intake vents below it. It's really a case by case question you'll have to judge for yourself. But make no mistake, fanless does not mean silently sealed up in a closed box. Fanless means increasing the number or size of cooling vents so natural convection cooling can work.

There is also the rather tricky question of what to do with all the heat dumped into the PC chassis by other components; the processor, motherboard VRM, motherboard chipset, videocard or IGP, hard drives, expansion cards and so forth. Seasonic have designed the X-460 Fanless to "be responsible for its own cooling and functionality". Choice words that perhaps don't underscore this point well enough - the X-460 Fanless power supply is intended to cool itself and only itself. Most computer systems rely upon the power supply to exhaust hot air from the top of the chassis, draw hot air away from the CPU thermal solution and motherboard's passive VRM heatsinks. What happens when that active exhaust port is removed?

The best answer we can give is that the Seasonic X-460 Fanless is not designed for these tasks and by virtue of its ventilation design will not absorb these tasks either. Thus while the Seasonic X-460 Fanless is built to replace any standard 460W power supply in terms of power delivery, it's not going to fulfill all the responsibilities usually associated with an actively cooled PSU in the computer system. It's a fine point of distinction, but a crucial one to be aware of should you embark on a totally fanless computer system build.

In and of itself, Seasonic have manufactured a very satisfying PSU that's evident the moment you lift it out of the box. The modular cables are sufficient for its power output, the build quality is enviable and it produces no noise from fans or humming capacitors. Retailing for about $160CDN ($160USD, £70 GBP), the Seasonic X-460 Fanless (SS-460FL) isn't cheap, but is well built, stable and efficient. It's a harder point to recommend or not, I think in this case a fanless power supply is one component best selected by DIY computer builders who know enough to answer that question themselves.

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