Can a regular jump starter battery charger be used as a 12v power sup

Yes, but be warned that the current delivered will be very high (typically 6 to 8 amps), so don't try powering small, low-current components/circuits unless you want resistors turning into light bulbs and microchips turning into miniature stoves.

However, if your circuit(s) are capable or rated to handle such current, go right on ahead. Some medium and larger motors are a great example of high current draw devices. Just be careful that the guage of wire in the motor (and anything else you're powering, really) is thick enough to handle the current, otherwise you'll end up turning the wire into a lightbulb.