Apple - current leakage of MacBook Pro?

The solution for me was to use the adapter with a three pin extension cord.

Then your notebook is earthed and no more charges stay on the cover that shock you :-). Some Macbooks suffer from insulation failure of the casing. A third contact provides for a connection to earth ground so that net charge can escape the cover. This requires a wall socket with proper earthing.

This is most likely due to an earthing problem. I used to have the same problem on my MacBook Air. To fix it:

1. Ensure that you're using the three pin socket converter.
2. Ensure that the connections are secure enough.
3. Ensure that there is proper earthing in your building.

For me, the problem was #2. I had to replace the (non-Apple) adapter that converts between US and Indian sockets.

220 volts is not the issue. The MacBook adapters are built to support it and the transformer within steps down the voltage appropriately.