Power Supply and Curious Outcome

This is non-critical. Just (to us) interesting.

I bought the following from a Roon Community member. I used to between the wall and my NUC.

Worked fine.

One night, I heard the NUC fan whirring away. The power supply was extremely hot. I took it out of the system.

I wrote to the manufacturer (cannot recall the brand but mentioned here in the past often) and offered to send it to him since it may be something that would interest him. I told him that I bought it used, that it had no warranty and that he did not need to return it but felt it may be interesting to him.

His response was…well…ungratifying.

So I still have it. I plugged it in (with top removed) and testing to see if it overheats again. It is not powering the NUC. It is just sitting on a shelf.

Any thoughts as to why it would have (after several months) become incredibly hot? There are no signs on the board or capacitor that it had burned etc.