That would require a catastrophic failure in the power brick which has significant separation designed in to the board layout to keep the primary line voltage side away from the secondary low voltage.

See this comparison teardown between a genuine Apple magsafe charger and a counterfeit, especially the "What's wrong with this charger" section: http://www.righto.com/2016/03/counterfeit-macbook-charger-te...

Related, Apple ran a discounted trade-in program where people could swap potentially dangerous phone chargers for safe ones after a counterfeit charger killed somebody: http://www.cbc.ca/news/technology/apple-replacing-fake-iphon...

With DC current you want to stay below 48 volts. There's a dog leg in how much damage you can do to a human being with electricity.

Well, from experience you'll be mostly fine with 100 VDC too. 100VAC is a different story though. (AC flows better into the body while DC remains on the skin IIRC)

There are legal limits, I don't think you can supply over 48V without entering a whole different regulatory structure.