There's lots of USB port accessories available in 12v format now. There are a couple advertised in the Wingworld magazine this month. I'm not sure how well a 120v inverter would take to the output of the Wing's charging system, especially if you plugged one into either the fairing pocket accessory plug or the trunk one, they are only about 5 amp circuits. USB is how I'd go.
all good answers.
Now, here is how it works....
your charging system puts out a certain number of watts.
Watts divided by volts equals amps.
This is true.
So in a home electrical system, you have a 110-120 volts at your receptacles. A blow dryer might use 1500 watts. For simplicity, let us say that 1500 watts divided by 115 volts equals 10 amps.
So yes, you can add an inverter. But figure out what the wattage is of your charging system, and subtract battery charging, lights, radio and such, come up with your remaining and then divide by 12 and you are left with your amperage available.
That is a rough idea. There are variables. Charging systems are not at 12 volts. they are closer to 14.5volts. And your electrical load is constantly changing depending on what you are using.
I still say you can install one, but yeah, using 12v based chargers are probably easier to use in the long run.
Most 12v chargers have a lower output and will take longer to charge your device though. your choice.