Quoted from lyonsden:
Yes -- I've connected many power supplies to various games. The key is to tap into an AC line that is after the main power switch to your game so that it turns on/off with your game. The dollar bill power is a good place, but you can always tap into the AC going to the main transformer as well.
Got the AC after the main power switch, am I right that FG is "floating ground" and is the ground circuit of the pinball not the mains ground?