Quite possibly nothing. A USB charger following the USB Battery Charging Specification has a resistor < 200Ω across D+ and D-. Just putting -200 V on D- and doi

Quite possibly nothing. A USB charger following the USB Battery Charging Specification has a resistor < 200Ω across D+ and D-. Just putting -200 V on D- and doing nothing to D+, there's not a completed circuit. If the charger uses the data lines for anything (e.g. Apple devices), perhaps it'd burn out whatever microcontroller is running things in the charger.