Understanding the effects of frequency on appliances
Magnetic iron cores are rarely efficient at spanning over a decade or maybe 2 of frequency unless ferrite.  So automotive alternators are not as efficient as fixed f types.  Eddy current losses tend to increase exponentially with frequency and Z also increases with f until self winding parallel resonance (LC).
200 to 400 Hz magnetics in iron cores have thinner laminates and ferrites also change composition with RF frequency with lower mu and more conductive particles. So the big torroids once used in audio power amps or SMPS are high mu until they start to exceed a certain f.
The main problem with magnetics and high current is if you lower the frequency too much, they can saturate and turn into resistors, so V/F ratios are used in variable speed motor AC controllers.
But if your are just thinking heaters, they work on DC.
Read the appliance label near cordset for safety approvals.