You could switch between two power supplies using the 3051 Relay Phidget
. You would connect the positive wires of both power supplies to your device's power terminal, and one of each of the ground lines of the supplies to the NC and NO terminals. You would use a wire to connect the C terminal to the device's ground terminal. This way, when the relay is switched one way, it will complete the circuit of one power supply, and when it's switched the other way, it will complete the circuit of the other power supply.
The relay board can be controlled by a 1018 Phidget InterfaceKit
, or any device with a digital output.