T38 is correct. I have never had a problem with non-motorized devices such as cell phone and laptop power supplies, but the potential exists. I have heard anecdotes of FAs burning out their chargers, but they use the outlet far more often then pilots on the CRJ because it's in the galley, not the cockpit.

Those vacuum cleaners that the cleaning people use do have 400hz motors. A 60hz motor would probably work...seven times too fast, for a brief period of time

You could step the frequency down using motor-generator arrangement, but that would be ridiculously complicated for the application.