It is possible you're thinking of the pass-through, because some keyboards, like the Corsair K90, have two plugs, one for the keyboard itself, one to power the USB hub it may have.
My old Logitech G15 v2 on the other hand had two USB 2.0 (maybe 1.0?) ports on the back of it but only had one plug for the computer, only some things worked in those ports.