I have this monitor.  It is possible to supply power with one usb-c and input video on the other (power on bottom usb-c).

"Why an AC adapter for power is not included in the box is particularly bewildering. "

What is so bewildering is the writer's inability to understand this! Why is it that all your reviews of such products question the wisdom of omitting such power adapters?

It's USB-C for heaven's sakes, not a proprietary power port. Everybody would either have such a port from their laptops or several power adapters and/or USB-C cables lying around the house already. Why would you want the manufacturer to include yet another power adapter in the box? Is the writer naive enough to think that anything in this world is free? It will only raise the sticker purchase price! Not to mention the environmental impact of the electronic waste!

This is a praise-worthy move that should be the norm for all manufacturers. There has been many campaigns for this to be mandatory to cut waste and reduce prices.

If it's not possible to use 1 for charging and 1 for video, why are there 2 ports? What's the use of that?

It's not possible to draw power from one USB-C cable while accepting video data from a second USB-C - have you tried a Y cable, you know one that physically separates power and video signal delivery between its two heads?? My guess is that you have not.