Reference +David Rich power extn things, two things (from memory not Google!) if you have a long lead the power will drop a little and the thinner the cable the more it will drop. All cable has a resistance, and of course it will depend what else is plugged in and how much that is pulling.

Dave mentioned his charger was showing as 87 but supplying 55, how does that change if plugged directly in? Does it show 87 or closer? If so, that is the answer.

As for extn leads heating up, this is pretty well known, and is basically how those bar electric heaters actually work, its a tightly wound cable which heats up :-)
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