Each power supply comes with a total wattage rating, but there's more to it than that. Power is divided among three primary lines at 3.3, 5, and 12 volts, and each of those lines carries a maximum current rating. To complicate things further, all but PC Power & Cooling's Silencer spread 12V power over multiple rails. Instead of opting for multiple 12V lines, the Silencer offers a single 12V rail with a massive 60-amp capacity.
Maximum output current (A)
|Antec EarthWatts 500W||24||24||17, 17|
|Antec Neo HE 550W||24||20||18, 18, 18|
|Antec TruePower Trio 650W||24||24||19, 19, 19|
|Cooler Master Real Power Pro 550W||25||20||19, 19, 19|
|Cooler Master Real Power Pro 650W||25||25||19, 19, 19|
|Corsair HX 620W||24||30||18, 18, 18|
|Enermax Infiniti 720W||25||30||28, 28, 30|
|OCZ GameXStream 700W||36||30||18, 18, 18, 18|
|PC Power & Cooling Silencer 750W||24||30||60|
|Seasonic S12II 500W||24||24||17, 17|
|ThermalTake Toughpower 700W||30||28||18, 18, 18, 18|
Amperage is only the beginning, though. Through Ohm's Law, we can determine the maximum wattage for each line, giving us an indication of actual output capacity.
Except it's not quite as simple as multiplying a line's voltage by its maximum current. PSUs with multiple 12V rails are limited by how much power can be spread across those multiple lines, and most units also limit how much power can be shared across the 3.3V and 5V lines. Then there's the total output wattage across the 3.3, 5, and 12V lines, which doesn't always add up to the maximum wattage of the power supply. Some PSUs reserve a portion of their total wattage capacity for lesser-used voltage lines like the -12V and 5V standby rails.
To make sense of it all, we've put together a handy table showing the maximum output power for each PSU's 3.3, 5, and 12V rails. Where applicable, we've also indicated the maximum combined 3.3 and 5V power, the maximum combined 12V power, and how much wattage the PSU can spread across all three main rails.
Maximum output power (W)
|Antec EarthWatts 500W||79.2||120||204, 204|
|Antec Neo HE 550W||79.2||100||216, 216, 216|
|Antec TruePower Trio 650W||79.2||120||228, 228, 228|
|Cooler Master Real Power Pro 550W||82.5||100||228, 228, 228|
|Cooler Master Real Power Pro 650W||82.5||125||228, 228, 228|
|Corsair HX 620W||79.2||150||216, 216, 216|
|Enermax Infiniti 720W||82.5||150||336, 336, 360|
|OCZ GameXStream 700W||118.8||150||216, 216, 216, 216|
|PC Power & Cooling Silencer 750W||79.2||150||720|
|Seasonic S12II 500W||79.2||120||204, 204|
|ThermalTake Toughpower 700W||99||140||216, 216, 216, 216|
These are the power delivery stats that really matter, and as you can see, the units vary quite a bit. Interestingly, only Antec's Neo HE and TruePower Trio make no mention of limits on combined 3.3 and 5V power. Among the others, CoolerMaster's 650W Real Power Pro is surprisingly the most generous, boasting 191W of combined 3.3 and 5V output. ThermalTake's Toughpower comes a close second at 180W, followed by units from Corsair and PC Power & Cooling. The 500W units from Antec and Seasonic predictably round out the low end of the spectrum with combined 3.3 and 5V output ratings of 130W.
Of course, 12 volts is where it's really at. There, PC Power & Cooling's Silencer tops the charts with a whopping 720W rating. The GameXStream and Toughpower PSUs aren't far behind at 680 and 672W, respectively.
Obviously, the higher-wattage PSUs are equipped to deliver more 12V power than the others. What's more interesting here is how each PSU balances the power it can provide across its 3.3, 5, and 12V lines. In a moment, we'll see just how well these PSUs react to loads that push their maximum output ratings.