[ltp] where in /sys is the power meter for my whole computer located?

[linux-thinkpad@linux-thinkpad.org]

I do
# iwconfig wlan0 txpower [0-20]
How can I see if this is really using less or more power than before?
I could check /sys/class/power_supply/BAT0/uevent but I am not on
battery power today. Where in /sys is "the power meter for my whole
house" located? I use Debian linux-image-2.6.32. I could check with
iwconfig but it just reports what I typed in.