Originally Posted by rhartnett35
So I have an NVIDIA GeForce GTX 550 Ti and I need a PSU to power it... I need 24A on the +12V rail, however I can not find this on any power supplies (I have a very low budget), however I have been able to find multiple ones in my price range with multiple +12V rails... so if I have 2 12V rails each with 18A, will this power my GTX 550?
In a word. No.
A little history:
As PSU manufacturers started to put more and more power into their products there was a concern that "the government" would get invilved (read: regulation) as it became easier and easier for computer enthusiasts to kill themselves.
So they adopted as a sort of volentary standard that they would linit the amount of power in any one "rail". The more unscrupulous manufactures (ie inexpensive PSUs) figured that if they gave people PSUs with 4 x 25 amps, no one was really going to use all four rails to the max all the time. So, they could supply a PSU advertised as 25 amps on each rail, but the PSU only had to supply a total of, say, 50 amps, since few ,if any, people need 100 amps total.
If the video card maker says you need 28 (or whatever amps) for their card, then you need that many amps.
Now, if you look at the name plate on a PSU it will list the amps it can supply to each and every rail, but if you add up all the rails (12V, 5V, 3V) you will almost always see that they add up to more that the PSU can supply. So, if it says 30 amps to a 12v rail that means that that 30 amps, PLUS what you are using from the other rails can't add up to more that the PSU can supply. And the cheaper the PSU the worse the things that will happen as to get closse to the limit of the PSU (to say nothing of what happens if you exceed it!).
The "more expensive" PSUs also have superior current controls and overload protection circuits. There's a big difference (in safety to your components and performance) between a $39.95, 300 watt PSU and a $200.00, 300 watt PSU!
Saving a few dollars on a PSU is an easy way to spend a lot of money on burned out computer parts.
Oh, and volts x amps = watts