They ended up with a gender bender cable. It was supposed to always stay attached to 1 bit of kit. That kit could run on 7-48V. Unfortunately, they unplugged it from the wrong end. When they plugged it back in, they put it into the 2nd power source connector. A 28V lipo was wired directly into a regulated 12V bus. That bus apparently was also connected to internal parts, and wasn't protected against backflow (defence in depth failure). Magic smoke was lost.