Controlling High-Power loads with the USB port is best accomplished with a combination of a large mechanical relay called a contactor and a solid-state relay controller.  When paired together, the computer can safely control the solid-state relay, and the solid-state relay will block the induction of the contactor from the computer.  Since a contactor contains a coil, it is an inductive load, and it must be managed accordingly with induction suppression components.  Contactors can be rated at many load and coil voltages, but keep in mind, most solid-state relays are rated for AC switching only.  A select few DC solid state relays are available, but care should be taken to choose a solid-state relay that matches the coil rating of the contactor.  We can assist you in finding the correct solid-state relay and matching contactor if you need help.