The basement came with several LED bulbs screwed into old-school ceramic sockets with pull-chain switches. This adapter had an LED bulb in its socket and another LED fixture plugged into an outlet:
The fixture began flickering some days ago, which I attributed to a problem with its power supply. When both the bulb and the fixture went dark, I had enough of a clue to locate the real cause.
The scorched plastic near the discolored weld nugget on the threaded shell suggests something ran overly hot in there for a while.
Peeling the aluminum shell off reveals the problem:
Looks to me like the weld started out weak and gradually fell apart as the socket heated / cooled in use, with increasing resistance producing more heat every time.
The LED lamp + fixture added up to 100 W, so about 1 A is all it takes.
The Smell of Molten Projects in the Morning 
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3 responses to “Lamp Socket Adapter: Weld Failure”
You might see if your insurance company will set you up with a Whisker Labs monitor:
https://www.whiskerlabs.com/
It listens to the noise and supposedly detects failures exactly like that. My insurance (State Farm) arranged for a two, since I have two panels.
The details seem deliberately well-hidden, but the box looks like they put the guts of an arc-fault circuit interrupter in a box, then interposed the InterWebs between the fault and me. Maybe their servers filter out false alarms, but the company seems intended to convert my insurance money into their revenue stream …
The no-name 15A receptacles in our manufactured house were sketchy, and after one released some magic smoke, I replaced them with good ones, probably Levitons. The manufacturer did use decent ones for the 20A receptacles, but the 15A and the light switches were pure garbage.