I think your red arrow is what you're after. Mine charges surprisingly slowly when it's on and flying/feeding my iDevices. In the hangar, I power it off, and run it off of a 2A cigar-lighter-from-AC adapter to get it back to 100% between flights.
I power mine using the data cable/direct DC cigar lighter cord. It's not a usb dongle thing, since I broke my micro-usb port off of the circuit board, for the third time. Annoying device at times.
I have a GDL39, but ForeFlight will tell me an actual battery percentage. I haven't tried with my Aera...
Interesting. I have 2.1A chargers (which I don't believe complied with an actual usb pd standard to begin with), but I've never seen one like that. I wonder if they forcibly mated a USB-C charging chip to a USB-A connector. I'd be curious to see what the actual current draw is; do you happen to have one of those inline usb volt/ammeter gizmos?
Anyway, glad you were able to get it up!
I'm pretty sure Chris Short can fix your GDL......he is amazing. Fixed my Aera 660, when Garmin wouldn't touch it!
@kgruber, did you ever test it out on that charger?Interesting that you should ask. I JUST bought this from eBay...