For UK residents, I bought this from Amazon, which arrived this morning. Claims to be genuine Microsoft manufacture, seems to be of decent quality (high quality feeling plastics and finish), and manages to charge the GPD while it is playing a 4mbit H264 stream in vlc.

Sadly the USB-C hub / lan adapter I bought isn't recognised at all in linux - nothing shows up in dmesg or lsusb. (CableMatter 201048). I can settle for regular USB-LAN but then I need to add a hub to use external storage for datalogging from Wireshark.