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Were you running high loads? I ran heavy, constant gaming loads with the monitor on (monitor specs say typical 140W, max 200W). After switching to the MBP charger, haven't had an issue for 5 years.

So it would be drawing 200W constantly. While it may have been a twice defective fluke, I suspect either the power delivery or heat killed it somehow.

The 100W MBP charger gets very hot by itself, and its twice that for the built-in monitor charger, which is also right next to the hot display panel. Add hot weather to the mix, and it seems like it could be trying to do too much.