The USB-C PD charger of my Nintendo Switch does not charge my phone, but it does charge my Surface. My phone's USB-C charger does charge the phone and Surface, but not the Switch. My USB-C battery pack charges my phone, but is charged by my Surface. Yeah, it just works.
How do, say, a battery pack and a Surface negotiate who is charging who over a symmetric USB-C-to-C cable?
The USB-C PD charger of my Nintendo Switch does not charge my phone, but it does charge my Surface. My phone's USB-C charger does charge the phone and Surface, but not the Switch. My USB-C battery pack charges my phone, but is charged by my Surface. Yeah, it just works.
How do, say, a battery pack and a Surface negotiate who is charging who over a symmetric USB-C-to-C cable?