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Does having a more powerful PSU affect me if my power draw is less than that?

I am putting together a new gaming PC and I was told I would be just fine with a 650W Gold PSU, but I can get an 850W Gold because I might add a few things in the future. My question is, that if having a more powerful PSU than the one that I actually need, affects my computer in any way. Will the electricity bill reflect the whole 850W, or just the 650W that my computer components actually need?

This is my build:

CPU:Intel Core i7-4790K
MOBO:Gigabyte ga-z97mx Gaming 5 (Full ATX version)
GPU:Gtx 980 Gygabyte Gaming 1
Noctua Ventilador NH-D14, S-1366, 1200RPM
RAM: Ddr3 Kingston Hyperx Fury 8gb 1866mhz Pc
HDD: Western Digital Caviar Blue 3.5'', 1TB, SATA III, 6 Gbit/s, 7200RPM, 64MB Cache
SSD: Crucial MX100 128 GB
Power Supply 3: EVGA SuperNOVA NEX 850W 80+ Gold Certified Fully-Modular ATX Power Supply
Case: Nzxt H440

Could you please guide me here? I don't think I will SLI anytime soon, but I will OC a moderately.

Thanks a lot!
9 answers Last reply Best Answer
More about powerful psu affect power draw
  1. Best answer
    It only pulls from the wall what it actually needs at that moment. 150W, 500W, whatever.
  2. sammael1984 said:
    I am putting together a new gaming PC and I was told I would be just fine with a 650W Gold PSU, but I can get an 850W Gold because I might add a few things in the future. My question is, that if having a more powerful PSU than the one that I actually need, affects my computer in any way. Will the electricity bill reflect the whole 850W, or just the 650W that my computer components actually need?

    This is my build:

    CPU:Intel Core i7-4790K
    MOBO:Gigabyte ga-z97mx Gaming 5 (Full ATX version)
    GPU:Gtx 980 Gygabyte Gaming 1
    Noctua Ventilador NH-D14, S-1366, 1200RPM
    RAM: Ddr3 Kingston Hyperx Fury 8gb 1866mhz Pc
    HDD: Western Digital Caviar Blue 3.5'', 1TB, SATA III, 6 Gbit/s, 7200RPM, 64MB Cache
    SSD: Crucial MX100 128 GB
    Power Supply 3: EVGA SuperNOVA NEX 850W 80+ Gold Certified Fully-Modular ATX Power Supply
    Case: Nzxt H440

    Could you please guide me here? I don't think I will SLI anytime soon, but I will OC a moderately.

    Thanks a lot!




    No it doesn't. It might imrpove actually. Since the 850W psu is gold rated and the 650W might be silver or lower the gold rated power supply has less power loss. But you need to stay at the optimum. I think between 40 and 90% load a PSU has the best efficiency.
    The PSU will only draw the power needed.

    Tl;dr: No it doesn't matter in energy cost.
  3. sammael1984 said:
    I am putting together a new gaming PC and I was told I would be just fine with a 650W Gold PSU, but I can get an 850W Gold because I might add a few things in the future. My question is, that if having a more powerful PSU than the one that I actually need, affects my computer in any way.

    As USAFRet has said, it'll only pull the power it needs. That build you've listed will pull around 400W, so with everything fully-loaded, the 650W unit will be at around 60% load, and the 850W unit will be around 45% load. Given that you're not applying more than around 60% load to the PSU, you'll find its fan spins more slowly, so will be quieter (good), and it'll probably last longer, as it's under less strain.

    One thing to watch, however, is that some PSU's are pretty inefficient at low load (<100W), however, this is unlikely to make a noticeably financial difference - a 10% difference in efficiency would make about a 5-10W difference (if you're curious, see if you can find a review of your PSU on TechPowerUp, as they have great PSU reviews, including nice efficency graphs, e.g. this).
  4. For instance, 3 minutes ago I took this pic.
    600w Corsair PSU, multiple FireFox windows open, several other things....

    104 actual wattage at that moment.


    Hover over my avatar for PC specs.
  5. i'd like to ask something here that is relevant to the OP's question so it isn't taking this thread sideways

    I work in a prototyping shop, actually i own it, but over the years we've had some electrical engineers come in on consultancy work, and twice i had an engineer, in relation to power supply sizing, indicate to size the power supply so that it's max output is twice the wattage that the equipment would be consuming on average - with the additional limitation of spike loads should not exceed 75-80% of the power supply's max capability. I asked one of those engineers (it's been a few years at least) why and basically he stated the efficiency aspect (as well as brought in the other current aspects which are greek to me) as well as longevity of the power supply.

    I've been assuming that's true here in computing, or am i wrong?
  6. The Original Ralph said:
    i'd like to ask something here that is relevant to the OP's question so it isn't taking this thread sideways

    I work in a prototyping shop, actually i own it, but over the years we've had some electrical engineers come in on consultancy work, and twice i had an engineer, in relation to power supply sizing, indicate to size the power supply that it is twice the wattage that the equipment would be consuming on average - with the additional limitation of spike loads should not exceed 75-80% of the power supply's max capability. I asked one of those engineers (it's been a few years at least) why and basically he stated the efficiency aspect (as well as brought in the other current aspects which are greek to me) as well as longevity of the power supply.

    I've been assuming that's thru here in computing, or am i wrong?


    That's pretty much correct. You never want the potential max load to equal the max output of the power supply. You ALWAYS want a buffer.
  7. thanks, but i am curious, are both those ratios the "demand to supply" ratios the computing field looks at in sizing a PS?
  8. The Original Ralph said:
    thanks, but i am curious, are both those ratios the "demand to supply" ratios the computing field looks at in sizing a PS?

    As stated above, optimum efficiency is usually right around 50%
    http://www.corsair.com/media//650txv2-efficiency.gif

    However, if you look closely at the labels on the vertical axis, you'll see there's not much difference in efficiency between 20%, 50%, and 100% load - about 83% efficiency vs 85% efficiency. So while it is optimal to get a PSU which is 2x your system's max wattage, it will probably only save you a couple bucks worth of electricity per year. That's a bad ROI if the higher-wattage PSU is gonna cost you $50 more.

    Most people aim for their system load being 70%-80% the Wattage of the PSU to give themselves some headroom. I would be very wary of pushing it to 90%, as the cleanness of the voltage delivered by the PSU can begin to deteriorate as you approach 100%. (Just to be clear, these are load percentages, e.g. a 450 Watt computer with a 500 Watt PSU = 90% load. These are not efficiency percentages.)
  9. thanks - i hadn't thought about in terms of efficiency or "ROI" but simply tried to keep it inside the parameters of what that engineer had indicated, but that would be a valid consideration.

    I suspect then i've overshot my PSU needs - max wattage draw on my computer has been 145W w/a gtx 750 Ti graphics card, while rendering videos, and my psu is a 450W seasonic
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