"Suicide cords" were a common alternative to that. Just a basic power cord, plug on one end, and a pair of clip leads on the other. Used to clip mains power to a transformer for test, or to get power to a power supply subassembly when the rest of the mains connections were in a chassis elsewhere.
I've never seen one. However any local hardware store sells replacement male plugs which open up and have three screw terminals. It would take a few moments longer than the wire clips in the Safeblock, but other than clip wires, I can have one on the end of a power cord in a minute or two.