Huawei P20 Pro charging in USB host mode

I'm seeing several related questions here. However, most of them are ancient (as in 2012) and refer to micro USB and maybe the USB-C standards are different with regard to host mode charging. I'm using my P20 Pro as a tactical flight computer with two connected devices. The first one is a single row mini usb keyboard and the second a flight vario which sends position and elevation data to the software. P20Pro | mini USB-Hub / \ KBD Vario What I'm missing in this setup is how to power the phone. I would need something like this: P20Pro |\ | \Portable Power Bank | mini USB-Hub / \ KBD Vario This is just some background info. The question could also be *How to charge the P20 Pro while a usb keyboard and mouse is connected?* Basically (at least according to Huawei's online chat support) the device supports charging in host mode since their MateDock 2 adapter also charges the phone. However, the MateDock 2 would be an overkill since I don't need a HDMI/VGA port. In addition I'm not sure what the MateDock is exactly and if it also redirects *non standard* USB devices. Another solution would be wireless charging but the P20 doesn't support this technology. So what is the the 2018 answer to charging in USB OTG host mode ?