Default [Q] Disagreement between USB power measurements

While charging via the OEM charger and cable, I measured power to my Samsung Exhibit II 4G T679 in three different ways:

- Kill A Watt P3 P4400 from Amazon, with the charger plugged into it

- "AboveTek" USB volt and power meter purchased from Amazon, plugged in just after the charger

- CurrentWidget app installed on the phone

Once it reaches steady state:

- Kill A Watt says 3.6W (if all this was preserved, then at 5V it would be 0.72A)

- USB meter says 0.55A at 5V (this is 2.75W)

- CurrentWidget says 1.1A (with the 3.7V battery this would be 4.07W

Needless to say, I am at a loss as to how these readings could be so different. I have tried it two ways -- with all three measurements going at once, and with only one at once. I always get the same results.

Which reading should I trust? Why do they appear so different?

For the record, I have also noticed similar phenomena with my Nexus 7. I could post those results in more detail if anyone would like.