To be completely fair, those power banks should have a diode (or some protection circuitry) to prevent their damage. A loose cable could easily put higher voltage on the port than 5.25V.
That said, what an awful USB port to come across. A little reading wouldn't have gone amiss though. My natural reaction would have been to assume it was an output, not an input.
That said, what an awful USB port to come across. A little reading wouldn't have gone amiss though. My natural reaction would have been to assume it was an output, not an input.