automatically reverse polarity of charger cable

Hey guys! I recently came across a product that has me puzzled. It's a little portable vape and it has a proprietary usb charging dock that has two contacts. Somehow it can be plugged in either direction, meaning the positive and negative pins are switching I guess. I've seen chargers like the MacBooks where the + is in the center and if you reverse the orientation it just pivots so to speak around that center pin, but this seems to do it differently. Any ideas on how they are doing it? I am interested in using this for a little project I'm working on.

Bridge rectifier on the unit being charged?

I'm not familiar with how that would work? If it's any help, the unit being charged is extremely small. The entire PCB is around 1cm squared.

Cool. I just looked at them and that makes perfect sense. Thanks for the input!

Of course a trickster would say - "its an AC battery!"