- Intel Core i7-870
- Asus Maximus III Extreme (P55, 0309 BIOS)
- 4GB OCZ DDR3 PC3-15000 / 1,866MHz / Platinum Edition @ SPD: 1,333MHz, CL7
- ATI Radeon HD 5770 1GB
- ATI Catalyst 10.1 WHQL
- Windows 7 Home Premium x64
Does using a more efficient PSU warrant a greater benefit than one that's "more appropriate" to the power being used? The efficiency curve of a typical PSU means that it doesn't become most efficient until it reaches 50 per cent load, however with modern systems using less than 300-500W under load and under 100W at idle, this means typical 600-800W PSUs can seem "too much" unless you’re constantly loading your PC with work. We also tested an older '80Plus' PSU against the most recent '80Plus Gold' of the same wattage to see what the real world difference is.
Click to enlarge
Seasonic X-750 (750W, 80Plus Gold)
Seasonic X-650 (650W, 80Plus Gold)
Be Quiet! SFX (350W, 80Plus)
PC Power and Cooling Silencer (750W, 80Plus)
FSP Everest Pro (1,200W, 80Plus Bronze)
Watts (lower is better)
We can see that the Seasonic X-Series 650W and 750W PSUs
- models that achieve 88 - 92+ per cent efficiency - really do benefit the system more than buying a lower wattage PSU. The 80Plus Be Quiet! SFX PSU is just 350W and it could power all the systems we threw at it, but it still used 3 - 4W more than the Seasonic at idle and 10 - 15W under load: a notable difference. That's not to ignore the FSP Everest 1,200W - at just 5-10 per cent of its rated power use, it is well into the initial upward gradient of its efficiency curve, and as such uses ~17W more than the Seasonic's at idle and 17-19W at load, even more than the 80Plus rated ‘lower efficiency’ Be Quiet.
Compared to the older PC Power and Cooling Silencer - which I must point out has been working relentlessly and flawlessly for us in our lab for nearly three years - the vanilla 80Plus efficiency means its power use is actually not as bad as the higher wattage FSP, however it's still ~8W at idle and 13-15W more under load.
If you think about it then, the efficiency of a new 80Plus Gold (or similar standard) PSU gives you three performance 7,200RPM hard drives, for 'free', but then you also have to consider the higher cost of such models - you’ll not easily work that money back through pennies saved on your electricity bill.