Six foot NES controller extension cable already modified into a RetroSpy cable. The cable splice uses 12″ Dupont wires about 1 foot away from the female end of the cable. The cable you receive may not work with the Power Pad, if that is an issue message me and let me know because I may be able to make one that does support it.
For a fully working RetroSpy setup you will also need a programmed microcontroller board. For instructions on setting up a board see https://retro-spy.com/wiki.