Yes the third prong is a ground. Will it work without it? Maybe, but I wouldn't recomend it! IT's grounded for a reason!!!! Don't mess with the grounding wire. Also I personally wounldn't run the power supply without some kind of case on it! What is this for anyway? If it's for a non-technical person I would say definately NOT. Too many stray fingers, etc... Especially if little kids might even POSSIBLY be around it. You'd be amazed at what some kids will do!