It charges great using the USB C plug from the iPad Pro 12.9”, but when I plug it into my trusty Anker 6 power power hub via a USB C to USB A, it doesn’t charge at all.
If I plug the same USB A to USB C adapter into a 5w iPhone charger with the MagSafe, it shows as charging (albeit I assume more slowly)
Does anyone know what the minimum requirements are?
I think it’s more complex than voltage or current. USB-C has a protocol for negotiating between chargers and devices. Since you’re plugging to USB-A, that negotiation probably doesn’t happen, as USB-A uses a different protocol that isn’t well standardized, and wasn’t part of the USB-A standard.