dtgreene: One thing: When the computer is mostly idle, or doing basic web browsing (not using anything like WebGL), how much power do these GPUs use?
Dark_art_: Surprisingly, higher end GPUs don't actually use a lot of power when in idle state, providing they are, say, 2017 and above.
Rant warning not even related to OP: Motherboards usually make bigger difference than GPUs. I don't have comparison data for the AMD X570 chipset aberration but the X470 chipset with all bells and whistles use 10-20W more at idle than a standard B350 (actual value depend on BIOS settings, CPU undervolted in both cases and similar memory speeds) with the same components and same overall performance.
While ̶A̶M̶D̶ Ryzen CPUs are
very efficient when loaded compared to Intel, however when taking all the pc parts on account, they still struggle to get the same efficiency on high C-states (idle etc) and light loads. I've seen plenty of Intel desktops (mostly OEM) idling at 15-20W, even old stuff. I can't recall a single Ryzen based desktop idling below 25 (talking about "gaming" typical components like i5's and R5's).
On the desktop GPU side, AMD was and still is a power hog with multi-monitor setups and video decoding. But to be fair, the Steam Deck integrated GPU is awfully efficient. The i5 on the Surface pro 7 needs
twice as much power to get similar performance as the Deck.
Integrated graphics is not always better in power consumption, infortunately. For a long time Intel has been stuck on 14nm CPU's and the integrated graphics suffer. A good example is some laptops with dual graphics 'low-power intel UHD' and some 'high-performance nVidia', on many situations using the nVidia GPU can get better overall power consumption than only the intel counterpart, including watching videos...
Do you have any actual figures? Also, any sources? Specifically, has anyone done any extensive testing on power consumption?