Smoked a 5/40e power supply

I was wiring a UPS to a 1771-P7 PS and let all the smoke out of it. I have wired 3 to 4 other PLC's the same way and had no problem. The power for the UPS comes from the same breaker in the panel that used to go directly to the PS. It was originally wired from the breaker to the PS and pigtailed from there to the cards in the rack. I put those two wires under a terminal and then came directly from the UPS to the PS. I'm still scratching my head over this one. The UPS is 1000VA Triplite (500w) UPS. The PS is fused at 3 amps so no overload there. I did a search on the boards but didn't come up with much. Could the UPS be out of phase with the supply power? Maybe getting a backfeed from the cards? I just want to keep the processor alive and well but isolate the output cards from the control voltage in case of an E-stop condition. Any ideas??

Output voltage

Most UPS units have both 120v and 240v outputs, have you verified that you are using the 120v output from the UPS?

check your pigtail and other connections look for a gound short. As well as checking the voltage output setting on the UPS