Originally Posted by cairastravis
I just opened up my old computer, and discovered it has the following 600W power supply:
Obviously it has dual 12V rails, but I already own it. So, have power supplies changed much since '06?
There are more single rail psu's available now to better work with the power hungry hardware available and sli/crossfire. Multi rail psu's are not as effective. Lets say you have three 12v lines each rated at 20a, this does not equal 60a on the 12v, in reality it's more close to 50a.
Let's take the picture you have there as an example:
Watt is Volt times Ampere. You have a dual rail system, 12v listed at 18 and 20a (38a)
That's peak performance. Since they list how much watt is dedicated to the 12v lines we can calculate the real performance on the 12v lines: 420w/12v= 35a
So lets say you max out the 20a line then you will only have 15a available on the second, or if you max out the 18a line you have 17a on the rail rated at 20.
A psu also loses its power as it gets older. So a psu that is a few years old might have lost 20% of its output.
Heat is also an issue the hotter the psu is less power it can provide, so it's a bad idea to cut it close due to both heat and age of the psu.
nVidia recommends a 500w minimum with 36a available on the 12v lines (432w dedicated to 12v). This is for the whole system.
According to benchmarks i've seen the gtx 260 can peak at 320w alone
EDIT: Good quality PSUs will not degrade in performance as much as a bad quality one.