USB 3.0 Standard-A plug and receptacle. A Standard-A USB plug inserts into a USB host, or a hub, and carries both power and data. The USB 3.0 Standard-A plug and receptacle are backward compatible with the USB 2.0 Standard-A plug and receptacle. A Standard-A USB plug inserts into a USB host or a hub and carries both power and data. USB 2.0 Standard-B plug and receptacle. A Standard-B plug typically plugs into a large device, such as a printer.