I've seen this before on some parts that failed- but I couldn't find a specific cause. On my last subwoofer I had a pack of resistors that looked like they were the source- but they all tested 'good'.
This is the power supply for a vacuum sealer. One of the chamber vacs you put a whole bag into, it evacuates the air, and then seals the top of the bag. It wasn't pulling a hard vacuum so I took it apart (again) to see if maybe the pressure sensing valve was bad. (I've subsequently remembered that there is no sensing valve in this unit, just a timer. Silly me).
Anyway, the power supply has a fine white coating on 1 of the capacitors, but not the other. It's also present on some smaller caps on one side and heat sink, but again not on others. Present on the bottom of the board in one spot that didn't have the insulating plastic too close to the surface- but again, not on others.
At first I thought a capacitor venting but doesn't appear to be any issues with the tops or sides. There is a metal film resistor near where the issue is but again, seems intact.
Any idea what I'm looking for here?