I recently bought an Ultra Compact Power Bank to replace my existing power bank and to use on long day trips. I wrote previously about how on my day trip to Venice I only planned to take my phone and the power bank. I also thought I should be able to charge my Apple Watch as well if that ran out of power.
Now the power bank worked a treat in charging the phone. Towards the end of that day I noted that my Apple Watch was down to 1%. So I retrieved the USB-C watch charging cable from my bag, plugged it into the USB-C port on the power bank and watched the watch literally not charge.
This time, when I went to Copenhagen, I took the USB-A charging cable that came with the watch and this (having tested it earlier) worked a treat in charging the watch.