A commercial device known as USB Killer 2.0 allegedly has the ability to fry a number of electrical devices by sending an electrical charge to a public-facing USB port. The device works by collecting power from the USB power lines (5V, 1 – 3A) until it reaches -240V. It then begins discharging its stored voltage multiple times per second. The recharge/discharge cycle lasts as long as the device is connected to a USB port. It will continue until it can’t discharge any longer when the device has damaged its host’s circuitry.
Source: https://www.bleepingcomputer.com/news/security/shocking-usb-killer-uses-electrical-charge-to-fry-vulnerable-devices/