The "AT" type power supplies I have are labeled 10 amps at 12 volts - between the yellow and black wires. My organist uses a Kit 67 speed control and a wiper motor. The current draw is just under 2 amps. I wouldn't load the supply to capacity, but you should be safe with two or three wiper motors and a few lights. You can buy a volt-ohm meter at Harbor Freight for $3 to $4 on sale. These will measure up to 10 amps. Check the current on what you are running.
Forgive a novice for asking so many questions..... Do the power supplies have some type of fail safe on them? If I connect to the improper wire on the wiper motor, looking for the low speed, the power unit shuts down. It restarts a minute or so later.
I haven't ever loaded a PS near to capacity, but you're probably right about some sort of internal overload protection. I checked another prop that uses a Subaru wiper motor to move the arms. If I try to hold the arms to load the motor, this one only draws 2.3 amps.