If you like living, then I would not use any wall transformer that is not rated "safe for use in medical equipment designed for human contact". Such transformers will cost at least $100.00 US.
Any power supply or transformer is subject to surges, breakdowns, or other failures and I for one would not want to be on the receiving end of 110 volts much less 220 volts!
I have heard that there have been deaths reported to the FDA from such occurences.