Dennis,
Well, for a PC power supply, the specs seem pretty impressive:
DC Output +3.3V +5V +12V -12V +5Vsb
Max Load 25A 25A 46A 0.8A 3.0A
It is always handy to have an extra +5V available too.
HOWEVER, 12V would not be my first choice. It will likely work well for smaller motors. You got the 305 oz in motors. At 12V you will not see the speed or torque these motors are capable of delivering.
I’d strongly recommend you power it with the max (36VDC) and at least 7.5 Amps to get the most from these motors.
These motors are a HUGE inductive load – they resist any changes in current, so one needs to really “slam” them with a high voltage (way over the 3 or 4 volts per winding in the specs) to really force the current to change quickly.
Summary: I wouldn’t use that supply in ‘production’, though it might suffice for testing, and it won’t do any damage.
BrianV