Just thought I'd share my recent experience with an eBay 20a 24v switch mode power supply.
I purchased this to use in my self playing piano project (if your interested you can see it here
https://youtu.be/xp2ocvnNoJs (this was a progress video its since complete)
The power supply worked ok for a little while but just had no output all of a sudden it was not under much load at the time of failure.
On further investigation the two large NPN transistors have failed shorted.
It almost looks like the board has been wet at some stage (not in the time I've owned it) the dried crusty flux everywhere is a bonus
Photos almost don't do it justice but I'm sure you get the hint. Enjoy