I (deliberately) flattened my iPhone today so I could charge it with its own charger. I about 19:00 I plugged it in to my kill a watt meter to see how much power it uses. I’m assuming the meter isn’t all that accurate, and as it is designed to measure typical household loads its display is in kilowatt hours.
With it plugged in for 19 hours with no load, the kill a watt claims to have consumed 240 watt hours. Which means that it would consume approximately 31.5 watt hours for a 3 hour iPhone charge time.
After charging for 3 hours the iPhone apparently used 40 watt hours, subtracting the 31.5 above gives a results of approximately 8.5 watt hours.
Given the inaccuracy of the devices, that is close enough to the 10 in my previous post for me to say about 10 and roughly in the ballpark of the previous test. Time to go looking for more accurate measuring devices.