Traditional cigarette lighters in vehicles operated on two principles.
One, traditional resistive heat. The element in a plug is just like any other electric heater, more or less.
Two, the expansion of metal when it heats. The female part of the plug had slots and ridges that made a pinched connection. The male part had a compression spring. So that when the element heated and expanded the compression spring overcame the pinch and the male portion popped out a bit and broke the circuit.
As the modern power port usually doesn't have the slots and ridges, the compression spring has no catch and accordingly can't pop out and break the circuit. So a male unit would sit in there until something got hot enough to melt and break the circuit. Most likely it would be the fuse...