Pixietown

My roommate's LED lights went out, and she traced it down to a bad wallwart. I thought I'd crack it open and see if there's any (electronic) gore.
Nothing on the trace-side of the PCB, nothing seems to have gotten super hot and burnt, unlike that last power supply I opened

And the top looks okay too, except maybe that cap on the left that's clearly on the way out.

(You may spot something else wrong. Hang on to that)

It's hard to see in the photos, but yeah, that cap is definitely bulging.

And then I looked at the top of the plastic.

HEY LOOK there's a cap. Or... the can for a cap?
It's stuck to the top, with the electrolytic fluid I assume.

SO YEAH it turns out that weird brown cylinder you've been seeing in the pictures is the capacitor. It actually exploded the can off it, with the can getting stuck on the top of the case.

it's also possible this was always like this from the factory. Maybe this cap is just used for smoothing, and it being exploded just meant it did no smoothing. Maybe the other cap was doing the same, and that's why it ended up bulging?

yeah. my knowledge of how caps work is limited (I only took the first semester of EE) but it seems to be between the VCC and GND on the DC side

so probably this thing was just outputting way less smooth DC than it should. Maybe the LEDs have their own caps, or maybe they just flickered like mad?

asking my roommate for updates

okay amazingly, she says it never flickered and never actually died: it just got dimmer.

so my guess as to what happened:

this cheap cap developed a partially short. It now began passing current through it. This caused it to heat up, boiled the electrolyte, and exploded the can off.

The thing STILL keeps working because now that it's dry, it's a really shit conductor, so only some of the current is going through the sploded-cap, which can no longer boil (and it doesn't get hot enough to ignite). But since some the current is diverted, the lights dim