There are a good amount of lower power ones (e.g. with an N100 CPU) that draw ~15W usually and not that much more at full bore, and some of them are starting to come with USB-PD power inputs (even if they come with a DC power adapter some will accept USB-PD on another port).
i have a passively cooled Quieter 4C [1] with N100 and a 4TB [dram-less] nvme [2] and it draws 4.5W total at idle running EndeavourOS w/ KDE Plasma. at full load (Handbrake 1440p transcode) it draws ~10W.
i left it at stock bios settings and did not put it into higher TDP mode though, since i use it as an htpc and it mostly idles, i'd rather it stay at more comfortable operating temps.
the nvme cost me more than the pc, which for $207 includes 16GB ram, 512GB nvme, and a Win11 Pro license. insane.
i'm mostly converting 4k from a phone to 1440p and cutting [backup] storage by 6x. most of these vids are < 3min, and i can do quite a few in a batch job overnight. im in no rush. it does about 4fps with the 1080p30 HQ preset with the only additional change to up the res to 1440p. i would not use it for batching feature length films, but you can do one in a pinch :D
Look for "PD in" on this sheet for some examples (columns BW-BY): https://docs.google.com/spreadsheets/d/1SWqLJ6tGmYHzqGaa4RZs...