I'm still thinking the field can dump an instantaneous current higher than what's available on the line, to fill a monentary request...
But I'm susceptible to moments of WrongThink.
I agree that what-goes-in is greater than the-usable-what-comes-out over time for all the reasons listed above.
Blow up a balloon (create the field), you can get the about the same energy and amplitude out of it over time or pop it for an exciting instantaneous bang...
I think the voltage will drop. In any case there seems to be an assumption (or its marketed as) that there is a requirement to supply enormous amount of instantaneous current from the mains. What we have measured so far is a relatively stable pulsed current draw which is essentially the reservoir caps charging. The caps is where the requirement is and where the current is supplied from when the ac cycle is a low/zero volts.
Just to gather some more info on this I am going to get my Onkyo AVR blasting at ear bleeding volume on all 7 channels and measure the dynamic mains current. Lets see what we see