but airliners do not supply 110/220 AC for pax use as standard
The trouble these days is that some do and some don't.
In the past 6 weeks I've used 110v AC seat power on Iberia (A343/346) and on Emirates (772.) I've also used AC power on LH (333.)
Some airlines use DC current (e.g. BA), but to confuse matters some airlines do both, e.g. BA where 10 A320s provide AC in club.
So caveat emptor and research is required.
My DC inverter also has a car adaptor (as I imagine the BA one may) so they can be used in the car on picnics and stuff - quite useful.