It's not the phone or iPad. they operate at very low voltages that don't harm you body. And it's in a case, there is no possibility of conduction, not even static electricity - they are designed to dissipate and conduct away triboelectric charge, to protect their sensitive electronics.
There is one scenario that could be true.
If you are holding is by it's metal/metallic case, and it is plugged into the wall, the wall-wart supply may have high ground leakage current, which is actually dangerous. If you put an AC voltmeter from the metallic case to the ground of a wall socket, and measure more that 60 volts, you've got a bad power supply. Take it to the dealer and show them. I'll bet they give you a free one immediately. The world electrical test labs ([link|https://sfgov.org/oca/approved-testing-labs-electrical-products|https://sfgov.org/oca/approved-testing-l...|new_window=true]) supposedly "approved your device for safe use. If it failed in some way, the big company that bought that sub-standard design is probably liable. I'm guessing they will want to replace it for FREE.