One way to change the direction of current flow is to temporarily unplug the cable and plug it back in. There is a kind of “memory” in Apple devices and their handling of peripherals that allows current to flow in both directions, if the current is not flowing in the desired direction, a “reboot” may be required by unplugging and re-plugging the Current reverses the flow of current. Some devices prefer power if the connected device accepts power. In this case, you should try a different tactic.
Using a USB-C/male to USB-A/male cable and a USB-C/male to USB-A/female adapter, you can construct a type of USB-C to USB-C cable. However, this USB-A port in the middle determines the direction of power flow, as USB-A does not support bi-directional power flow like USB-C.
The USB-A port limits power flow to 12 watts, which shouldn’t be much of a problem since a MacBook Pro’s USB-C ports deliver a maximum of 7.5 or 15 watts, depending on the model and other connected loads.
I’ve heard of people trying to charge USB-C power banks from a laptop and watching the power bank charge and then discharge. It seems that the decision about where the power should go is “reset” by both devices when left unattended, because once the power bank’s charge level reaches full charge, one device or the other decides to send the power to the device to transmit in the opposite direction. A USB-C cable with this USB-A port in the middle avoids this because reverse power flow is not allowed through this USB-A port.
There may be USB-C to USB-C cables that have hardware that limits current flow in one direction. However, this is a cable that does not meet USB specifications. I consider such a cable to be convenient, but since it lacks the USB trident logo to indicate it meets specifications, I may not trust it.
