Startechcom usb to 34 to 55mm power cables type hmn barrel startechcom usb2typem the startechcom usb2typem 1m usb power cable makes it easier to power 5v dc devices that have a type m barrel power connector od 55mm id 21mm you can power or charge the devices through an available usb port on your laptop or desktop computerthis usb power cable could save you having to carry around a separate wall adaptor in order to power or charge your 5v devices such as certain external har