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Picking the Right Power Supply—How Much is Too Much?

By Will Greenwald

Hardware rules of thumb dictate that more power is better. But is it possible for a power supply to be too powerful?

Hardware rules of thumb dictate that more power is better. The more juice you can keep consistently flowing to your components, the smoother your system will run. A wimpy, tiny power supply can cause all sorts of problems by not feeding your components enough electricity. Crashes and glitches can occur if your power supply isn't up to snuff; in fact, the word "glitch" in electronics refers to unwanted electrical pulses that can disrupt circuits. Logically, you want a power supply that can put out as much electricity as possible. But is it possible for a power supply to be too powerful? 
 

 
one generic 500W power supply could only put out 250 watts, and died when they tried to draw 275 watts. Brand-name power supplies like Thermaltake and Silverstone should be favored, even if their maximum rating is less than a $50 generic you see on eBay. 
 
"sweet spot" of power consumption is between 60 and 85 percent of your power supply's maximum rating; if your system's maximum power consumption is 450 watts, you should get at least a 550W power supply. If your system's maximum power consumption is 600 watts, you should get at least a 750W power supply. Calculating your system's potential max load isn't difficult--most component websites show you how many watts their parts will need on a full load (eg. max TDP for CPUs and GPUs).
 
There's very little reason to get a 1200W power supply when you're building a 400-watt workstation, but besides the initial cost, as long as the power supply is well-made, there's no real disadvantage to it. According to Anandtech, efficiency can vary between different power supplies, and a more efficient power supply will be more economical in the long run, but there's no real correlation between power supply size and efficiency. The low-power (300-500W) power supplies showed that the 300W models were generally more efficient, while the high-power (600-800W) power supplies showed that the 800W models were more efficient. It simply varies between power supplies.