25-30 yrs ago I used a TI-58C handheld programmable calc w/dual-voltage charger (115/230 manual-switchable) from the flight deck outlet. The charger was a simple transformer/rectifier type, not auto-sensing like today's devices.
Anyway - even though the charger was labeled 50-60 Hz, it didn't mind the 400 hz at all. In fact, transformer theory tells you that it should run cooler on the higher frequency (lower iron losses).
And today's auto-voltage-sensing charger rectifies the AC line voltage directly to DC before feeding a switching-type power supply, so it too should be quite tolerant of the 400 hz.