We think it was a laptop or cell phone on charge. Marshall won't say yet.
My neighbor is a service electrician. He's good at chasing weird problems- found a broken neutral on my drier 220v outlet. It was about a foot above the panel and caused by a staple driven in too tight. I found it when the foil vent arced against the j-box.
We see issues with Chinese cloned stuff/chargers etc that is not UL rated. bathroom fans and fans we use in our shops. I drive my wife crazy as we unplug the coffee maker, microwave and toaster every day. When we leave for a trip a lot of breakers get turned off. paranoid? a little but I have worked a lot of fires on the outside and inside of the office and it is pretty tough when you hand a personal property form to an insured and say I can replace material things but I cannot replace you pictures, memories and special items. Get with you agent and look at you coverages and LIMITS on certain items