I am confused because the apple support article says "To use both the iPhone and Watch charger at the same time, the MagSafe Duo Charger requires at least 15W (5V/3A or 9V/1.67A), but this will result in slower charging.". So that makes me think it would work with 18W usb A ports. However it also says USB C only? There are USB A PD adapters that deliver up to 18W. I attempted some tests myself on some chargers I have that have 18W usb A ports and have only gotten the duo to work using a usb C port. How does it know I wonder?