We are all here to help, and I wish to offer some advice in the most gentle way possible. You have gone through some weird operations of trouble-shooting that have wasted your time and made you confused and frustrated.
First, you swapped out an entire system, and the problem was probably just the incoming power. You still don't know if that's really the original cause. Now you suspect that the power supply is damaged, after all.
Finally, you are using up your time by pulling out cross-connections and re-terminating them ???!!! For goodness sakes, wouldn't it be more efficient to just go around and unplug the phones? Or unplug them right at the KSU?
Now that you think you have a reliable UPS, by-pass it, and plug the system directly into commercial power. (Have you measured the power at the receptical?)
Do you have (from one of your earlier attempts) a spare power supply? Can you swap it in a reasonable time frame?
