*Originally posted by: ***John**
*Originally posted by: ***Scoop**

For the love of god you don't need a 750W PSU for that, are you serious? The only thing it's good for is giving a bigger number on your electricity bill. You're fine with your current PSU.

Actually that is a misconception. A 300W load on a psu is the same no matter what the wattage rating of the psu listed as. It's the efficiency of the psu that plays a vital role on the amount power that is required from the wall socket. That 200W load on a 300W psu that is only 70% efficient will require 429W from the wall, and if the 750W is 80% efficient it will only require 375W. Therefore in this case the higher wattage psu saves you money on your electric bill.

1000(kWhr)/54(wattage difference)*.15(cents per kWhr)*24(hours)*365(year)=$70.96 (yearly savings)

What math are you doing to calculate the wattage pulled from the wall?

By my understanding, a 70% efficient PSU transfers 70% of the power from the wall into usable juice for the PC. So to figure out how much wattage a 70% efficient PSU needs from the wall to supply 200W to the PC, we use this equation:

.7(x) = 200W

Dividing both sides by .7, we get that x, the power from the wall, equals ~285W.

For the PSU that's 80% efficient, we start with this:

.8(x) = 200W

and find x to be 250W.

There's still a difference, but it's smaller than you made it out to be. I'm wondering where you came up with 429 and 375.

Regardless, this has nothing to do with the size of the power supply, only its efficiency. Also, my understanding is that some PSUs are less efficient if they're running below half of their maximum load, which may make it

*less* cost-effective to run a larger PSU. (This depends, however, on the particular unit's efficiency curve.)

As far as the original post, a modern computer with a dual-core processor and an 8800GT draws at most something in the neighborhood of 200-250W from the wall at full load. A

*quality* 400W PSU is plenty to power your upgrades. Your old PSU is probably sufficient, assuming it can supply the necessary amperage on its 12V rail(s). If it can supply more than 25A using some combination of the +12V rails, you should be fine.