During my flt ops engr career, I regularly charged my TI-58C handheld (I'm dating myself...) using a 400hz source near the jumpseat. The charger was a simple transformer-rectifier device, and in general, transformers designed for 50-60 hz are perfectly happy (cooler than normal) on 400hz.
The converse IS NOT TRUE - there's not enough iron in a 400hz transformer to permit it to run at lower frequency. 400 hz transformers (& motors, generators, etc), because of their lighter weight, are popular in aircraft.
The switching-type power device for a laptop first rectifies the incoming AC to DC to drive the switching semiconductors. It should not matter what the power frequency is; 400 should be as good (or better) than 50-60 hz.