Within the context of USB Power Delivery , it needs more than simple power and ground to actually work. While it’s theoretically possible to make such a device

Within the context of USB Power Delivery , it needs more than simple power and ground to actually work. While it’s theoretically possible to make such a device that would determine which device is the source and sink, determine voltages and charge rates, then smartly select one and begin charging without the devices directly communicating, no such off-the-shelf device currently exists as far as I’m aware. You basically want a USB PD firewall that would only allow commands relevant to changing through, or have it generate synthetic responses that would e.g. never allow it to expose things like a mass storage interface. You might also need drivers depending on how you implement it. It would be a cool project / crowdsupply / Kickstarter though. More info: http://www.usb.org/developers/powerdelivery/ http://www.usb.org/developers/powerdelivery/ Right now, USB-C is only just starting to get past the “which cables will physically harm my device with a given charger even though they plug in correctly” phase.