Oh, I didn't know that. Thanks for the info mate. Regarding the second PSU however, wouldn't the amps per rail be lower than the one I recommended, seeing that it has three +12V rails compared to the one I proposed?

So when a PSU has multiple rails just add up ampage on the 12a 12b etc to find the maximum you're capable of running? sorry short message at the in-laws

No.
On the psu label itself you need to find the maximum wattage amount on the combined 12v
Or some are labeled as total maximum combined wattage and then give you a figure for the combined 3.3 and 5v. You would have to subtract that amount from the combined total to get the 12v amount.
This is an example for my psu: different psu's are labeled differently bear in mind
Dell 305w psu (OEM)
DC OUTPUT: +5V /22A, +3.3V /17A
+12VA /18A, +12VB /18A
-12V /1A, +5Vfp /2A
this is the most important info
+5V and +3.3V shall not exceed 150w
+12VA and +12VB shall not exceed 264w

This is taken directly off the label of my psu, so to figure the amps:
264 divided by 12 = 22
My psu is 22amps which is pretty good for a 305w
Don't be misled by a psu that claims it's 500w, do the math and see why it costs only $40, hope this helps

I didn't know myself, mate. I spent a whole day trying to figure out how Dell sells their XPS line configured with the 8800's with a 375w psu and duals in sli with a 450w psu but this is how, there are quality made and supply the amperage needed. The are some Dell owners that run 7950GT's with the same psu as mine(305w). Go figure?

Here's a good link to a site that figured all the amps for many psu's. It seems to be pretty accurate:

http://forums.guru3d.com/showthread.php?t=205763

Fantastic, thanks everybody, got everything I need to know now, all I have to do is wait another 3 days until payday and I'll be able to throw my FX5500 in the trash, oh baby can't wait...

wondering if you guys could help me i have this psu

octigen.com/products/productdetail.asp?Id=13&A=3&B=4&C=#

do you think be enough to run a 7600gt

# Input voltage: 115V-230V
# Input current: 6.5A
# Total output of +3.3V and +5V shall not exceed 152.8W
# +3,+5V and +12V total output power maximum is 296.8W

i get 24.73 amps that right?

No, you have 12A provided on the +12V rail by that PSU, making it far too weak for the 7600GT, which requires a minimum of 18A. You'd need a new PSU with a +12V rating of at least 18A and a total power output of 350-400W.