I've heard that that is not the healtiest thing to do to your PSU, as there is no load on the 5v and 3.3v lines for PSU #2, and switching ATX PSU's are designed to operate with a load on all rails. cooler master included a dual PSU harness with my CM stacker, all it does is connect the "power on"(green wire) and a ground wire to the second PSU in order to give it a simultanious power on signal.