Same question on reddit a while ago

As suggested there, I recommend to use a multimeter to identify the power socket pins. Roughly half of them should be ground. Most or all of them should correspond and be connected to the SATA power connector pins on the other side.

+1 on that. The User’s guide of a similar device (source) mentions a 10-pin CPLD connector Reserved for IBM use

Syncthing on Android has an option to only sync when on AC battery. The PC client might have a similar option. If not, you could probably configure something similar via systemd or udev under Linux.

I don’t think syncthing has proper means to synchronize contacts or anything else that’s not file-based though.

I use syncthing and prefer it for synchronizing files between my devices.