My friend has two PCs connected to same UPS. SMPS of one of these broke down while other one is running fine. On opening it, he found the Mosfets are shorted. He asked me as to why did this happen. Had it been a surge etc it should have caused both to die (both of same make). I gave him these reasons. (1) In any current boost switching circuit, if dead time differs then mosfets will be shorted. This means your SMPS controller IC caused it. (2) Could be the thermistor or dried up electrolytic capacitor. Am I correct in my reasoning?