What is wrong with having a massive power supply for a low power system?

[John_The_Channel_Unnamed]

when you have a system that would only need say 400w of power and you use a 1000w PSU, what are the advantages and disadvantages excluding cost of the psu but including cost overal of electricity

 

[ThatVietGuy]

You're just wasting money - that's really the only downside.

There would be no change in your electricity usage - you'll use the same 400W of power regardless of whether your PSU is capable of outputting 500W or 1000W.

 

[esco_sid]

That would depend on the efficiency and quality of the PSU but generally you want total wattage + 30% PSU for most efficiency.

 

[Scottray]

Besides efficiency, PSU's are designed to operate in a range where load regulation is maximized and ripple is minimized. Thus, there is a small probability with using a poorer quality, high power PSU in a low power range, that you'll get some glitches.

 

[Ecky]

Power supplies have an efficiency curve. Here's a sample from 450w and 850w versions of the same unit:

Consider for a moment that the system in my signature idles around 30 watts and draws about 160w under torture testing (from the wall). At these low numbers, the efficiency difference between a low and high wattage unit might add up (just ballparking here) to around $1-2 per month if you leave your PC on all the time, or ~$10-25 per year in electricity. Considering I've had my machine for 5 years, an oversized unit could have cost me as much as $125 in electricity at the very highest end estimate.

EDIT: The Platinum-rated unit I'm using cost me $25 after rebate, and replaced a similar wattage bronze-rated power supply. I expect it'll pay for itself, nevermind that I sold the unit it replaced.

 

[alceryes]

The only benefit you *may* receive is that your PSU might have a longer life running at only ~50% utilization.

I've been using an old BFG 800W for the past 8+ years now. Never pushed it anywhere near an 800W draw. I check the rails every once in a while and they're always good. I know it will eventually go, just not tonight.