> Also, a bad USB charger should not kill a device.
Then you've not seen bad USB chargers. Of course a device that by design is pumping voltage could ruin whatever it is connected to - especially if the connected device is sensitive equipment.
I've seen a USB charger pumping -1 to 11 volts AC out the USB connector - it was fluctuating 6 volts in either direction. Of course, you need an oscolliscope to detect that as it's at 50 hertz (C plug) - on a regular voltmeter it looked like 5 v steady.
Also, a bad USB charger should not kill a device.