As in many other observations one can easily see how much more efficient it is to remain DC throughout the entire charging process.
To go from 0% SOC to 100% SOC using straight DC>DC, as opposed to DC>AC>DC we saved 1.28 Ah's of energy (5.64 Ah - 4.36Ah = 1.28)!!!
Put another way when using the 400W inverter and Apple 120V adapter to charge this iPad it uses 29% more energy to for a complete charge cycle.
Total Charge Duration = 4:41
Total Energy Consumed = -4.36 Ah
Average Current = 0.8A -1.1A
So what's the bottom line?
If you want to charge as efficiently as possible, stay with DC!