In article , "Danny D." wrote:
Danny D. wrote, on Tue, 01 Dec 2015 00:20:57 +0000:

The voltage and current fluctuate so, even if you pick the
RMS voltage and current of the one AC signal, if you try to
add it to another AC signal with a different phase, then
you have to factor in the power factor.

This article says the AC power factor plays a role whenever the
AC current and the AC voltage are not in phase:
https://en.wikipedia.org/wiki/Power_factor

I think the whole power factor thing is a red herring because
we're talking output power, which is DC, which has both the
current and voltage in phase.

Only if the 40W is for the input power would the AC power factor
matter, and, if that 40W was for the input, it wouldn't be called
Watts - it would be called VA (volt amperes) anyway.

?? The definition (or one of them ) of watt is W=VxA (or VA). Are you
saying they are different ? ... if so, why ?
https://en.wikipedia.org/wiki/Watt

(snip)