This isn't an iPhone we're talking about, this is the charger which is connected to 220V AC power. The chargers are build very small, and cheap off-brand chargers have insufficient clearance between the LV and the HV side. This is dangerous, and can cause the 220V mains to go through to the USB port. This is also a very well-known property of cheap phone chargers, and you can find many teardowns online that show what I'm talking about.

https://www.youtube.com/watch?v=wi-b9k-0KfE

https://www.youtube.com/watch?v=dfJ3Ui8IS04

http://www.epanorama.net/newepa/2016/10/25/cheap-usb-charger...

I have also seen a few videos of teardowns of actual faulty chargers. For example, there was one where some of the insulation in the transformer windings were damaged, and you would get a continuous shock just by touching the LV side of any devices that are plugged in.

> that's why you can't electrocute yourself by putting your fingers on a 9v battery even though it's well over 200mA.

If you break the skin a 9v battery can kill.

http://www.darwinawards.com/darwin/darwin1999-50.html

Exactly. If you create a 9v voltage between an artery and a vein (though 0.1v is plenty) and you generate more than around 160mA current (any battery and static electricity can do that).

Essentially you'd have to get a conductor into an artery and one into a vein, and if there is a millisecond where both are in there but not touching the skin your heart will stop. It can be restarted for a minute or so afterwards, but it won't restart on it's own.

Your skin has a "safe" (more or less) conductive layer to prevent this from occurring, with another layer with enormous insulation below that. That's why humans usually survive getting hit by lightning, yet succumb to such a stupid tiny amount of current if it gets past the skin.