@pythno IIRC ou can `$ watch -n1 cat /sys/class/power_supply/BAT0/power_now` to get the instantaneos power usage and probably some other file in /sys/class/pci/your_gpu_pci_bus/state to check wether your gpu is in D3cold (sleep) or D0 (awake and active). And for me the problem was a bad config with drm modesetting. Basically i just read the arch wiki and tried stuff that seemed somewhat relevent to me and my laptop until it worked...
On nvidia nvidia-smi was useless since it wakes up the gpu...