Remote control Power Supply

I'm quite new to using an Arduino and electronics generally.
I'm using an Arduino Uno with adafruit micro servos and 16-bit PWM shield.

I have code that uses the serial moniter to control a servo for on off positions. Is there a way I can switch the power to the servos (from external power supply) off?

So the power supply is off until I send a command to move the servo and then afterwards switch the power supply off again?
I have an idea that you could do this with a breadboard, but I'm not sure if this is the best method to do so.

I don't care that the external power supply still sends power, I just don't want it getting to the servos when its not neccessary.

Many Thanks,