I use a device similar to this. Pretty useful and handy.

Probably the easiest way. It’s plugged into a smart plug with energi monitoring.

Them probably uses a special plugin device in the outlet.

I have this bash script you can use and have a general overview but I’m not totally sure if I fully understand it and if it’s the whole system’s wattage or only the CPU 🤷‍♂️

#! bash
time=5
sum_1=$(cat /sys/class/powercap/*/energy_uj | awk 'BEGIN { sum = 0; } { sum += $1; } END { print sum; }' "$@");
echo "before" $sum_1
sleep $time;
sum_2=$(cat /sys/class/powercap/*/energy_uj | awk 'BEGIN { sum = 0; } { sum += $1; } END { print sum; }' "$@");
echo "after" $sum_2

sum_1f=$(printf "%.0f" $sum_1)
sum_2f=$(printf "%.0f" $sum_2)

final_sum=$(echo "(($sum_2f - $sum_1f) / 1000000) / $time" | bc -l)
#echo $final_sum | bc -l | xargs printf "%.2f\n"

formated=$(echo $final_sum | bc -l | xargs printf "%.2f\n")
echo $formated "w"