I have gotten shock from my iMac for years, even when I plug my phone in. I have checked the Internet and could never find a fix and still got shocked after I tried everything. So I took a good look at the plug, and the ground part is very shiny, look like it was lacquered. So I sanded the ground prong very well, cleaned it, plugged it in and haven't had a shock in months. Just a public service anouncement