Using a computer power supply to power 12V devices is common, especially among computer efficianados with high-currenet 12V devices. Be aware of two things:
ATX power supplies will NOT work out-of-the-box. They are designed to be switched from the motherboard, so you will have to manually modify the motherboard cable with some simple circuitry to "trick" the PSU into believing the motherboard has instructed to turn it on. Older AT power supplies do not have this feature and always supply power when they're turned on.
Also note that most power supplies are designed to provide power to a computer as a whole, with typical balanced power on 5V, 12V, and other supplied voltages; if you leave all the lines unloaded and load the 12V side down, some will not work at all and others may give varying results (eg, 14V or 10V output, something like that.) It's hit or miss; DIY hobbysts don't sweat soldering a resistor on a 5V wire to balance the load and if you're just jerry-rigging an old car radio, this could be the way to go, but I wouldn't do this for something critical.
Considering how many of these things are sitting "free" on junk piles of old computers, it's very tempting, isn't it?
[This message has been edited by SteveFehr (edited 12-15-2005).]
[This message has been edited by SteveFehr (edited 12-15-2005).]
