Your desktop’s power supply converts the AC power from your home or office into the Direct Current that your PC needs to operate, then distributes that power to each component. So needless to say, it’s pretty mission critical. But what does an individual Power Supply’s wattage or its efficiency rating even mean? And how much wattage do you need in your next dream PC?
Wattage and Efficiency
To start, power supplies have two basic ratings to be concerned with – wattage and efficiency. The wattage is simple; it’s the maximum amount of power the supply can output when under a 100% load. So a 600W power supply can distribute UP TO 600 watts to the PC’s components.
The efficiency rating is how well (or how efficiently) it converts the AC power to DC, or to look at the other way, how much power it wastes during that conversion. For example, a Bronze Rated power supply, which by definition must be at minimum 82% efficient at full load (with higher efficiency at lower loads), will output 82% of the inputted AC power to DC, losing 18% of the original wattage to heat. That means that a 600W Bronze Certified PSU with its 82% efficiency will draw about 730W in order to output the 600W.** Higher efficiency power supplies like Bronze, Gold, and Platinum aren’t just great for energy savings, but also tend to last longer because a less severe heating/cooling cycle.
**Remember, that’s only under full load – a PSU will only draw what it needs to.
More info on efficiency level certifications can be found in this handy Wikipedia entry.
Matching Wattage and Efficiency to Your Custom Components
A critical element to the configuration of your PC is ensuring the PSU you choose is robust enough to output the power needed to run the components that you’ve selected, with a bit of headroom to spare. Consistently maxing out your power supply is not the best recipe for system longevity, after all. Here is a very rough list of the estimated power consumption of your vital PC components, though obviously these numbers will vary for each specific component.
- Mid-range graphics ~165W
- High-end graphics ~350W
- Mechanical Hard drives ~9W each
- Solid State Hard Drives ~3W each
- Haswell CPU ~75-90W
- Haswell-E CPU ~140W
- Motherboard ~30-80W
- RAM ~3W per stick
- Optical Drives ~25W
As you can see, the graphics card (or cards) will be the biggest power draw in your PC with some top end graphics pulling 350W+ each while under load, although significantly less at idle. But even with several hard drives and a Haswell CPU, a 600W power supply is sufficient for most single GPU configurations. For multi-GPU systems, we typically recommend at least an 850W PSU, with 1000W (or more) needed for 3x GPU configurations.
One last note – when choosing a power supply, it’s important to select something that will not just meet your current needs, but also something that will suit you for any planned or possible upgrades. Plan ahead!