Re: "Magic smoke"
I used to have to troubleshoot AT&T/Avaya "Merlin" and other phone systems. (They were amazingly reliable overall) Sometimes I'd have to verify a wiring path was intact, and I also worked on their networking for their Terminal Server/dumb terminal environment. All jacks were RJ-45 and often times things were not labelled well, if at all. I used to buy a few of the cheap $10 cable testers with a remote unit off ebay and keep several on hand. The reason being if I would plug them inadvertently into what I though was a serial or Ethernet jack, but turned out to be a phone jack fed from the PBX, the 48V would instantly fry one of the lines on my tester. I went through about 5 of these in the 4 years I did that job. The dumb terminals were resilient to the treatment if plugged into the wrong jack, but once in a blue moon it would damage one of the cards in the phone system.
I made a point of labelling everything I encountered and using different colored jacks for each if I needed to replace them, but a surprising number of employees would just plug in anything wherever it would fit. "A hole is a hole." ..without getting too deep or off topic, I think that logic applied beyond networking as well to many of them.