I wish all cameras could charge with USB-C; it makes for great convenience sometimes plus with two batteries in the Fujifilm GFX100 battery tray, charging by USB-C charges them both overnight. I’m unclear on whether the charge is low battery first then the other, or one battery first by position then the other, or both at the same time (the GFX100 drains one battery at a time when shooting, as is the smart thing to do).
I found that the Anker PowerCore+ 20100 USB-C Charger Battery charges the GFX100. GFX100 batteries are rated at 10.8V X 1250 mAH ~= 13500 mAH or about 13.5 watt hours while the Anker unit is 74 watt hours, so it should be able to charge a GFX100 battery 5 times, or probably 4 times with charge/discharge losses if the batteries are totally drained.
Which means I can take along the Anker battery and a USB-C cable in the field for extra power I have 3 batteries for the GFX100, which likely will not be enough for a day. The Anker battery can also charge the Sony A7R III, so it can do double duty.
See my review of the Anker battery in Anker PowerCore+ 20100 USB-C Charger Battery.