I'm not sure whats the quality of your PSU, but what I'd do on an unknown PSU (including those for computers):
1. Connect up voltmeter parallel to the 12v rails
2. Add a 12v load: maybe a 12v fan or two.
3. Fuse in series with your 12v line: I think 10A is more than enough?
4. A switch [S1] in series with your 12v line just BEFORE your control systems
So you turn on your psu first, but leave S1 off. Check the voltage and if you're happy, turn on S1. Reason being some switching PSUs start off with a voltage >>> 12V for a few milli/micro seconds immediately after turn-on and may fry your stuff. Just a precaution
