400 Hrz. Outlets
I concur with FullWings entirely. As the chief technical Captain for no less than three airlines I have repeatedly encountered this issue and discussed the matter with both Boeing and Airbus.
A very simplistic way to visualise the problem is this:-
If you laid out 400 paving slabs end to end to a garden shed at the bottom of your garden, you could walk effortlessly to your garden shed. Now consider laying out a pathway of 50 slabs alongside the 400. To take that path would require a great deal of energy as you jump from one slab to the other. 400 slabs in this case represents your 400Hrz. circuit and 50 slabs represent the 50 Hrz. circuit. Thus the energy supplied by the system to power your 50 Hrz. device is increased.
I have encountered on two occasions where the running of 50Hrz. units has caused the main ground power circuit breaker to run hot, but not enough for it to trip. However, the continual use in this condition lead to premature failure of the ground power circuit breaker. This is a NO GO item, Why? Because:-
On most big Aircraft the ground power circuit breaker supplies the Fire Detection and Extinguishing functions, loss of this circuit leaves you with no way of extinguishing a fire on the ground AND in flight.
Let this be known to all Cabin Services Departments who think they can just introduce DV players, telephone battery chargers an the like to the aircraft electrical system without a properly approved and certified modification. They CANNOT.
Some aircraft are modified to except 50Hrz equipment through special outlets, in particular to supply medical equipment. No doubt more modern aircraft will come with compliant power outlets. If you don't have such outlets you cannot use the 400Hrz supply unless you are using a certified appliance.