PUt a meter in line with the motor and try it to see what amperage it is drawing. There is an off chance that the breaker in the power supply is going off at too low an amperage. The behavior you describe sounds just like an overload. Does the power supply have a short indicator? And does it come on when the motor stops? If the amperage goes way up, over 4.5 or so, it is probably the motor. If the breaker trips at 2 amps or so, then the power supply breaker might have an issue. 56 VA should give you more than 4 amps at 12 Volts if all on same throttle.
If all your other stuff is newer (2000s) give or take, they might draw less than 2 amps and the breaker may ignore them.
