Mike Tomlinson wrote
wrote

Of course even a well designed charger
doesn't meet that naive expectation.

And to prove Woddles wrong (again):

https://www.youtube.com/watch?v=3Hdn0MuCK_0

Doesn't prove me wrong. That transformer clearly wasn't properly
designed. It was never properly designed so that a manufacturing
fault couldn't see full mains voltage on the USB. A much better
bobbin design that keeps the primary and secondary completely
separate so that no manufacturing fault could see it end with a
direct short between the primary and secondary of that transformer
could occur.