Gotcha yah I was thinking of the ‘balance charger’ or hobby lipo charger style charger since it’s what I use (no BMS and lipos) but not sure why it would happen with a regular laptop power brick like that perhaps there something more than just a couple of coils in those as you’d have in a regular transformer.
Did some googling since this sparked my interest https://superuser.com/questions/338263/is-it-normal-for-the-laptop-charger-to-spark-when-plugging-in