[otter-rock]

There are actually three parts of the power triangle: real (W), reactive (VAR), and the hypotenuse apparent (VA) power. If voltage and current are exactly in-phase, VA=W and VAR=0. All of the power is doing work.

Being out-of-phase is like turning a crank with one hand while resisting with the other - wasted effort. Some of the VA becomes VAR instead of W.

The math thing is a simplification so you can take measurements with a multimeter, and do just a bit of arithmetic to get all three power values. It comes from the average power integral of trig functions with complex numbers.

Watt rating is what you'd expect. Voltage and current are working together to do work. The limit is probably thermal.

VA rating at max current is a short-circuit. If your load draws enough reactive power, the voltage and current get so far out-of-phase that a huge current sneaks through without much voltage. It could be many times as much current as the max current at max Watts.