I just installed this USB charger socket from Amazon, and it works just fine on the stock 6 volt positive ground electrical System on my Model A. It even has an on/off switch.
【Upgraded Version】Car Charger with Switch, CHGeek 12V/24V 22W Waterproof 2.1A & 2.1A（4.2A）...
https://www.amazon.com/dp/B07SGJ5DN4...sms_tai_4EiRDb...