Soon I'm going to live in a house alone with my girlfriend, it's up to me to pay the electricity... I was going to do SLI or Crossfire when I decided to buy all these powerful components. But when she came out the 9800GX2 and the 3870X2 I abandoned the project and I preferred the dual GPU solutions. Now I wonder how many watts does my powersupply to support the consumption even of future dual GPU GTX Fermi from nvidia ? 750 or 850 ? Because 1000 Watt seem excessive to me. I dont have more than 3 HD and a CD player to feed

Switching out a PSU won't help you save on the electricity bill. If anything your 1000w will be more efficient at running what you have.

your pc will only draw as much power as it needs efficiency is the only factor that will save you money on electricity bill

Everything stated above is true. Now let's get really technical: Moving to a smaller PSU (assuming it's not too small) would mean that his system power draw would be closer to the peak of the efficiency curve of the smaller PSU. Example: let's say a system needs 250W DC under load. A 1000W PSU may only be (let's say) 80% efficient at this load while a 500W PSU may be (let's say) 85% efficient. So switching to a smaller PSU may in fact yield some power savings. Now, just because it saves some power doesn't mean you should switch. The amount of $$$ you'll save is actually quite negligible. I did the math and assuming 24/7 operation and that electricity costs $.15 per kwh and using the example above, you'll save $24.09 per year. If you only run the computer for 12 hours per day, cut the savings in half. If you only use it for 6 hours a day, the savings are only one fourth of that original figure. If you don't have your PC at full load the whole time it's on, you only are saving one eighth of the original figure. And if electricity is cheaper, this figure will fall some more. So under what I call 'typical conditions', you're looking to save about $3 per year purely through power savings. Even though the savings look small, consider looking at this from a purely financial situation. Your current PSU is certainly worth more than a smaller unit. It may be benificial to you to sell your current one and purchase a smaller unit. If you buy a used PSU, I'm thinking you could get a smaller PSU plus keep about $100 in your pocket. Finally, back to your original question. No, it's not worth it to upgrade your PSU for the sake of lowering your electricity bill. (Unless the effort of making the switch is worth $3 in your pocket, anually.) However, switching PSUs may prove to add some cash to your pocket right now. That was so overkill

I thought I read somewhere that if you have the right wattage, you achieve a greater efficiency than one that is rated much higher? I think 500-600 watt is enough for most systems even when running dual card.

I understood but I am still confused with the overclock of the CPU consumes more ? So even with a wattage calculator can not know exactly.

In the case of a larger PSU, cooler means more efficient. Efficiency ratings are based off of what the PSU does at full load, and with that comes heat to the internal area of said 600 watt PSU. Plus we havent even hit on cap aging, and what power is left of your 600 W after a year or two of abuse. I have to go with rocker on the 1000W being the better choice, especially if its already in the rig. In order to save power with this PC, if it isnt folding or cruching 24/7, shut it off.

yes the more you push the parts the more power they require to do the job. Some of the online PSU calculators allow a section to OC your CPU's and see just what the proc will draw. http://extreme.outervision.com/psucalculatorlite.jsp I took the liberty to input your settings and it shows ur Q draws 137W to run. Same rule applies to an overclocked graphics card

Thanks sneeky, then there is no point in changing PSU because consumption falls if you do not use load and gaming 24H.

Overclocking the CPU increases how much power the system as a whole will use. So the higher your OC, the more electricity you use. That's what I was saying in my post above. Efficiency in modern PSUs is a curve peaking at about 50% of it's rated capacity. So a PSU is most efficient at about half of its rated wattage. So at a 250W DC load (which is typical for most systems) a 500W could easily be more efficient than a 1000W PSU. Heat is directly proportional to efficiency. (which you have said) But I don't see the relevance here. While that's true, we're only talking about efficiency. And I would assume that capacitor aging affects all PSUs equally because we don't have a way to measure this. As long as the PSU used is around ~40% more than power draw, I would assume that cap aging would be able to use this margin. I agree with your conclusion, but I don't quite understand some of the points you've made?

at idle the PC can still draw quite a bit when overclocked, but no where near what it pulls at load. Like I said, if it needs to save you money, shut it off when not in use. @ Angelkiller... point is more that if you have lets say a 500W and a 1KW PSU on the same rig, and the rig pulls 400W. The 500W PSU is going to run alot hotter to produce the 400W to the PC than the said 1KW. Again as the age of the PSU goes, the caps wear out and produce less power as they go. So after a couple years you are left with a 425W PSU pushing for 400W or a 925W PSU, again still running cooler and still quite able to handle the job

It isnt scientific fact, but I would lay $5 on the fact that it is no less efficient than getting a newer lower wattage model.

PLEASE do the math before spending more money. check how much power your system consumes (cheap watt meter, kill-a-watt or similar), check how much power you will save per month with a new psu, check how much of a difference that will make on your power bill

If you have a 1000w psu, it doesn't constantly draw 1000w from the wall... say your system only draws 450w at load, your psu will only draw 540w from the wall (assuming it's 80% efficient)