As much as I understand, AC is more efficient for long distance transmission and much more versatile because it allows to be transformed from one voltage to another. To have AC you obviously need it to periodically reverses direction (otherwise is just DC), and for everyday appliance the frequency at which this happens is 50 or 60 Hz mostly for historical reasons.
So once you plug a device this contains a simple rectifier that change the direction of one of the ripple so that the signal is more akin to the DC (usually) needed for the device to work.
Also, I've read that in the old times the supply signal was used as the frequency reference for devices that needed it.
So, all of this raises a question: what happens if you feed a (for example) 50Hz device with a 400Hz supply? Is there something implicit in the rectifier so that it can work only at specific frequencies? Or will it still work and just happen to produce a "more DC" supply (that is, with less pronounced ripples)?