You probably already know if not than now you'll know that there is device called "USB Killer" which can kill your electronic devices like computer, laptop, phone TV and so on in matter of seconds.
How does it work?
Well, although it looks like normal USB (flash driver) but it doesn't have any memory in it, instead it has high voltage capacitors and some other stuff which step up the low (5v which the usb gets from the device) voltage to more than 200 volts (it depends how it made) and then sends that high voltage back to the device.
Why devices die?
It is quite obvious that when the high voltage current goes through the USB port it burns some of the components on the circuit board and then the whole system stops working.
At the moment most of the electronic devices we see don't have protection against this killer usb built-in (in the future companies might add the protection feature) but in the meantime you can use USB adaptor which will hopefully protect your device.