Some of the Sony Vaios actually do require the ground, or you'll feel a mild electrical "tickle" when your hands are on the case. I think Sony may have fixed this problem in later models -- it certainly isn't an issue with mine (I've used it with the 2-prong Sony travel charger and I'm using it as we speak with my Targus which, though 3-prong, is plugged into a 3-to-2 adapter).