In my entry illustrating the practical difference between CPU TDP and actual power draw, I used a Mozilla program to read Intel's RAPL (Running Average Power Limit) CPU information. In that entry I regretted that as far as I knew there was no AMD equivalent, so I couldn't get similar measurements on my AMD Ryzen based office machine. Well, it turns out I'm wrong about that. Courtesy of @thurloat@mastodon.club comes this information:

@cks WRT <my entry>

this project might be useful to get some readings, came up in the AUR when I searched for a rapl package to install after reading your post. https://github.com/djselbeck/rapl-read-ryzen

The repository calls it a 'a quick and dirty hack', but in my testing on my office machine, it appears to work (ie, it appears to produce plausible readings, both under no load and under 'mprime -t'). In its current form, it appears to take an instant reading of the current power level, although I'm not sure I completely understand what's going on in the code.