I checked and it was all the way back in 2009 when I began to monitor the mains power consumption in our apartment.
So imagine my excitement when I found that I can now also monitor in detail the power consumed by any USB gadget on charge.
Hot foot from Maplin UK has just arrived the USB Power Meter. At 30GBP plus shipping cost it was somewhat overpriced so I had to search my soul for some considerable time before ordering.
Here is the full manual. Click on images to enlarge.
Closeup of Back
Closeup of Front
So I just ran around the house looking for things to monitor. Here is a small ad hoc table
No great surprises. Notice how the iPad Air makes good use of the special 12Watt charger to replenish its extremely large 8827 mAh battery.
Now I am off to find some more devices to monitor. What fun.