People always go cheap with connectors. Really it looks like there was a surge down the line. Check those filters and regulators. And check the grounding on the connector. I have a feeling that the connector head did not provide enough insulation and got melted because of it.
It looks strange to me. There are five conductors, yet the burn seems fairly uniform all the way around the housing, not oriented around any conductor or group of them.
The plug seems massively damaged but the notebook socket not so much - the crap there may even be just debris from the plug and not local damage.
Did some contaminant get into the plug before it was connected? Coffee? Maybe the cat tinkled in it? I'd have to see one before guessing further, and a few details, such as whether that plug ever worked would be nice.
I have the G5 iMac (the one just before they went Intel) and it is a real pleasure to use on lots of fronts but the peace is a big one. I used to turn off my PC in this office and breathe a sigh of relief, you sort of don't realise how that fan noise can make you crazy...Skronker get one! Then we can MacChat!
Spend a few days inside a factory that does a lot with metals. The noise is repetitious and constant. After a couple shifts, the noise doesn't even leave your head when you leave the factory. After a week, it insinuates itself into your dreams.
That foamy look around the connectors makes me think that something like Coke was spilled on the connector. It still shouldn't have gotten so hot though.