Power Supply Subjected to Heat or Over-Heating

It depends on a lot of things. My experience is that one component sensitive to overheating is the electrolytic capacitor. I.ve seen electrolytic caps mounted above power resistors that failed due to the heat.

Neither, the thermal overload protection would disable the power supply module.

High impedance would be seen at the line side and (most likely) there would be a reversed biased diode (anti-parallel or freewheeling) seen across the output side.

Unlikely, though if it did one would expect the appropriate circuit protective device(s) to disconnect the fault.

...thereby removing the source of power that would be contributing to the overheating.

...thereby making them individually the best source of information on these pieces of equipment. It's worth a couple of telephone calls.

When you say an energised power supply module you need to be a bit more specific as to the type of module. Do you mean an encapsulated module with only input and out terminals and terminals for adjustment or a module made up of discrete components, sometimes on multiple boards?

The integrated module can suffer from degradation if they are effected by heat when energised but they normally have a phase back protection where the output current is decreased as the temperature rises until they reach the point of shutdown. However excessive heat can cause a catastrophic failure evidenced by the internals evicting themselves from the casing.

Adverse heating with insufficient heat sinking can lead to deterioration of components such as Electrolytic and polyester capacitors, doides, voltage regulators and most other semiconductors.

I have replaced diodes that have failed either shorted, opencircuited or in very annoying cases they have acted like a resistance. Similarly voltage regulators that change their characteristics and do not regulate at the desired voltage, but some value other than desired voltage, leading to unusual output voltages or current control.

Opto couplers can become opto decouplers or require more drive. Many semiconductors can go into thermal run away where they just turn on harder and harder until they and what they drive become expensive bin fillers.

Should a cooling fan fail semiconductors overheat, the smoke escapes, which we all know drives electronics not electrons and you have an ashtray or a tray of ash. Capacitors subjected to overheating lose value and then pass excessive ripple current or even turn into tinsel makers, great for Xmas but not for power, when they explode.

As to the results of overheating they can be anything subject to which component fails and can only be characterised by the damage they cause, the blackened circuit board and the acrid air defreshener.