To read the current power consumption on my system76 laptop, there
is currently no file called /sys/class/power_supply/BAT0/power_now.

To read the consumption on the battery, use the following instead:

    $ cat /sys/class/power_supply/BAT0/current_now /sys/class/power_supply/BAT0/voltage_now \
	| xargs \
	| awk '{print $1*$2/1e12}'

Remarks:
  - Will print the current power consumption in Watts
  - Will not work when battery is not used (when on AC)