hi, the smaller USB socket, shaped a bit like a D on its side, is a "from USB Host device" it is a powerless socket, ONLY for the transmission of data from another device,usually a PC, the flat straight USB socket is a "To device" and supplies a small current as well as data transmission, and because of this power supply you can plug in, portable hard drives, floppy drives, lights, etc etc..unfortunately your keyboards do not have these, so you are restricted to data transmission only.