hey bros,
i have the exact same issue.. the exact same chiller and the exact same plug..
yes, i realized it was because it was not grounded.. i changed to so many adapters and configuration to find the best adapters with grounding.. but it didnt work
however, i got myself a grounding probe and ive never felt the electric shock..
however, there are days i remove the grounding probe to "test water" .. the problem seemed to have disappear.. so im not sure what happened,lol
or maybe there is still current in the tank but i cant measure it without a kit.. just that i dont get electric shocks anymore