Originally Posted by Arthurrs
Well, it depends on the design of the power supply and the computer itself, and unless you know the condition of the equipment, it's best to be careful, that's all. The likelihood that your equipment develops a ground fault is extremely minimal at best, and having an external "puck" or wall wart supply can possibly make the risk even less, since it keeps the AC mains outside of the computer. No need to have a paranoia about it!
Yes, it does depend on the power supply; linears being the obvious type without electrical isolation. I just checked every puck device I own. They are all 2-prong with the exception of the iGo Juice. The lack of a ground prong, coupled with UL approval, leads me to believe that there is in fact electrical isolation between the AC & DC sides of the puck. Granted it's been 20 yrs since I designed power supplies for a living and equally as long since I last looked at the relevant UL stds. Without dismantling the iGo, I would bet a 110v shock that the only reason it has a 3rd prong is that they cannot anticipate that every adapter they replace will be 2-prong (litigation prevention).
I'm well aware of the potential risks with floating ground. I just don't see it as a problem with a 2-prong puck.