ATX power supplies regulate off the 5V rail, they dont regulate the 12V rail.If you want to use one as a general power supply, you have to modify the supply so theregulation is done from the 12 V rail.If you dont the 12 V rail will sag when you put any kind of load on it.
Your power supply is rated for a total of 350W. You won't get all 350W out of the 12V supply.As a comparison I have a 400W ATX Supply on my desk. There are two +12V supplies (as specified by the ATX spec), one rated for 14A and the other for 15A (which can vary). Since you can't just tie two regulated outputs in parallel, we have to go for the higher current supply. 12V * 15A = 180W. That sounds weak for a 300W audio amplifier.Also, keep in mind you may need to load your 5V supply (like with your resistor) so the supply will turn on and regulate its other outputs.
One of the guides I read specifically answered that question and said you could..?
(It's rated for 18A on each of the rails).
I still don't understand what the previous person was talking about with regulating though, I haven't been able to find anything on that.
Quote from: steven6282 on Jul 08, 2012, 09:27 pmOne of the guides I read specifically answered that question and said you could..?Not everything on the Internet is correct. When it comes to many things people try something and it appears to work "fine". Regulated supplies in parallel with each other start to play tug of war with each other. It will work in some cases, especially cases where you aren't fully loading the supply, but will likely cause one of the regulators to fail eventually.Quote from: steven6282 on Jul 08, 2012, 09:27 pm(It's rated for 18A on each of the rails).Yes, but not all at the same time...P = I * E = (18A * 4) * 12 = 864 Watts. (That number look strange?)Quote from: steven6282 on Jul 08, 2012, 09:27 pmI still don't understand what the previous person was talking about with regulating though, I haven't been able to find anything on that.The original ATX Specification did not require the 12V rail to be regulated. Initially it was intended to drive motors and fans which weren't really sensitive to the exactly voltage being supplied. However, as more of the VRMs started running on the 12V rail, I would expect the 12V rails to be regulated now.
As for the number looking strange, not really. Should it, if so why?
And the last part, umm that really didn't help explain what the regulating is.