Hi, I bought a PC case that needs a top mounted power supply and so obviously the power supply can't extract heat from the bottom. I bought a GTX 460 too which requires "at least 24 amps on the +12V rail. So I have had a hard time findig a PSU that extracts heat from the rear and has 24 amps on the +12v rail. Only ones i found had 22 amps on the +12v rail or didn't specify. I'd also lke the PSU to be relatively cheap as I'm trying to do a budget build. less than £20 maybe. Thanks guys. (EDIT) Must also be at least 450W
Your problem is this, wattage is important, but the second is even more so as you have found out the amount of amps a Psu can deliver across the 12v power rail.
There in lies the problem, because a cheap PSU for around £20 will never be able to provide 24a let alone its full wattage stated.
Because put simply cheaper electronic components are used.
Think of it this way the key component that links all of the parts of the computer is the Psu.
If you buy a cheap one it is likely that if it becomes faulty there are very little safe guards or protection to isolate it if things go wrong.
The end result is, it takes out the rest, or most of the other parts of the computer when it gives out.
So add up what it would cost you to buy a new motherboard, a Gtx 460 card plus all the other things.
And you see why people say never buy a cheap unbranded Psu.
If you ask most people it is a common lessen they have learned, through prior experience of using a cheap unbranded psu.
And why it makes sense to buy a good quality one.
After all it should last a few years. and if of a higher wattage and amp rating, be ready for any future upgrades or use with another build.
Here is a link to good power supply take note of all the power protection included, most likely a cheap Psu of £20 will not include most.
Two 12v power rails at 18a combined is 36a total.