This is strange for the IEC supply, as it has an earth terminal. Are you sure the outlet it's plugged into has a good earth?

The 2-prong (unearthed) adaptors will cause the empeg to float at roughly half mains voltage - but with very low current flow (almost anything will earth it, but if you touch both a grounded object and the empeg you'll feel a tingle).

Actually, my Vaio (also being metal) suffers from this exact problem as it only has a 2-pin PSU. I used to get tingles from my (earthed) empeg when holding a (floating at ~100v) serial cable connected to the laptop...

Hugo