Got it. The port connected to A7 adapter is the Sink only port, thus you need to put a 5.1 kOhms resistor on its CC1 and CC2 pins. After the adapter detects the resistor, it will send out 5V on VBUS then the board is powered from A7 adapter. If you want to see more details for this kind of adapter (Type-A plug to Type-C plug), you can take Type-C Specification as reference.