Not just the batteries. User supplied power bricks sounds like an incredibly bad idea at pretty much any scale.

Wait, power bricks are a fire hazard?

Yep. Reputably manufactured ones (Dell, HP, Apple, etc) are probably fine.

But the cheapo replacement ones that you see people buy from Amazon, Ali Express, Ebay, etc... can be really not good. :(

User supplied ones are. Frayed wires galore

Not sure why the comment above is downvoted, but I have been twice in the same room with somebody's power brick starting producing fumes while dying.