Yes I have the same problem, when I touch the usb plug and the empeg at the same time I get shocked. I also have the little power supply, but Im shure that the problem is that the outlet the both are plugged into, its not grounded. I live in a historic house built in 1892 so I dont think they knew what grounds were check you outlet with one of those little tester thingies with the three neon lights to see if the outlet is properly wired, the reverseing of the hot and neutral could also cause this. Most power back ups and surge protector power strips tell you right on the front if the outlet is properly wired too.