I live in an old home without ground (three prong) receptacles. How important is this to be using an adapter that operates a pc without the ground of the POWER PLUG connected?I think VERY important, but Fed and Homer are the electricians. Perhaps they will be along shortly.The point of having an earth is to avoid electrocution. It's up to you to decide whether or not you think this is of any benefit... what rob said is correct. the point of a grounding prong is to avoid electrocution. if there ever is a problem in your power supply, and the hot wire TOUCHES your computer case, the whole case will become energized. without the grounding wire, the circuit breaker will not turn off and therefore presents a shock hazard.

grounding is not necessarily crucial, but it is a lot safer.

P.S. there are ways to ground old recepticles if you really feel the need for the plug to be grounded.Thank you for that. I guess I really MEANT is it important to the computer operation, not the safety of people nearby. Will NOT having that ground prong connected damage computer FUNCTION? Thanx.Very possible...the computer not being grounded will not effect the computers function.