Ungrounded laptop (Macbook Pro) buzzes in headphones, weird feeling when fingers brush lightly

"I am an electronic engineer, living in Korea, and thought I don't have/own a Mac, I use a number of USA electroinc items in my electronics lab. I have indeed seen this problem frequently. I'm not a power supply expert, but it appears to be related to the way 220V outlets are powered here versus how they are powered in the USA. Here, one of the two ""hot"" prongs is actually a neutral (nominally at ground potential), just like our 110V outlets in the USA. In the USA, however, our 220V outlets both prongs are ""hot"", neither one is at ground potential.

I haven't worked out in my mind exactly what's going on. Without getting deeper into circuit design theory, the fundamental problem is that the power supply, having no ground reference. has to guess where ground should be for the DC output. Some do a better job than others. I've measured supplies whose outputs floated from 30 to 90 volts above ground. In most of these cases, the extra voltage was enough to prevent other connected equipment from working, and often enough to ""feel"", as you are feeling on your laptop.

I would recommend finding any buying a three-prong, grounded third-party power supply. It's unbelieveable that the manufacturer would just say ""oh, that's normal"". Yikes!"

"So, I went to a reputable authorized Apple service center here in Korea and they basically said that this is normal and happens with every ungrounded, aluminum bodied Macbook. I was able to feel the effect with other laptops in the store. I'm currently living in Korea. I don't think Apple manufactures a grounded plug adapter for their external power supplies for Korean plugs. Really, it only seems that in the last two years that Apple has really regarded Korea seriously, so maybe they'll come soon.

I guess that's that. I'd still like to hear an explanation for what's creating this effect. Also, they said that some people can feel it more than others."