My secondary rig is a Core i5 10400 mini-ITX system with a RX5600XT. Still need to finish rebuilding it properly but I estimate full load power consumption to be well under 300W at the wall.The biggest power consumption part would be the GPU. My main system is a Ryzen 7 5700X and an RTX3060TI. The latter consumes at worse around 330W from the wall. I use an SF600 PSU but its quite clear a 450W PSU would be enough for my system.
If you are going for a lower power consumption gamig system,I would base it around an RX6600. The RX6600 is very efficient.
Use a CPU such as a Core i5 12400F or Ryzen 5 5600/5600X capped to their nominal TDPs,and use an mATX motherboard based around a midrange chipset(B660 or B550). Full ATX highend motherboards might not be as efficient especially with higher end chipsets. I would estimate such a system would be fine with a decent 450W PSU.
Also look at the efficiency curves of the PSU at lower loads under 50% or thereabouts.