So for my new build, components here. I've decided to go with the Corsair 850HX power supply.
Based on the components I've selected, some of you may say this PSU is overkill as I'll be running 2 SATA HDDs and one NVIDIA GTX 275 card. I don't plan on running more than 1 video card and I'm not a gamer but I do do photo/video editing and VMware.
My thinking is upgradability. When the new NVIDIA cards come out, they'll probably have higher power requirements than the current 295 cards. I simply don't want to have to upgrade my PSU for the next generation video cards. I've also upgraded from the TX series to the HX, I like the idea of a modular power supply to eliminate cable clutter.
My PSU question for this post: Will the 850 use more electricity than the 750 when idle? Meaning, does the 850 use more power off the bat or is it just capable of 850 W when needed?
I've learned a great bit from these forums and have changed a few things in my build as a result of the numerous posts I've read.
For the past 4 years there has been a big push within the commercial IT community to go green and save energy. We're finally seeing that filter down to the gaming community. A good example would be the new ATI Radeon HD 5000 series of cards. They require less power.
We will be seeing more of that. Manufacturers are working on 32nm dies which looks very promising. In addition they are working on embedding the video gpu right into the cpu which eventually "might" mean the disappearance of video cards.
Anyway, to answer your question, the power supply will only draw power that is needed by the system. Whether you have a 500 watt power supply or a 1000 watt power supply, if you are only using 300 watts during a gaming session that's all each power supply will draw. If lowering your electric bill is what you are concerned about, then take a look at the brand new psu's that earned Gold certifications for energy efficiency. Of particular interest are the brand new Seasonic X650 Gold and X750 Gold 100% all modular power supplies:
The general rule of thumb is a high quality 500 to 550 watt power supply with sufficient current (amps) on the 12 volt rail(s) can easily power an overclocked Intel Core i7 system with any single video card made. A high quality 700 to 750 watt power supply with sufficient current (amps) on the 12 volt rail(s) can power an overclocked Intel Core i7 system with two video cards operating in dual mode. There are a few exceptions like the new ATI Radeon HD 5000 series cards which use less power due to their energy efficiency.