Danny D. wrote:
Dave Higton wrote, on Mon, 30 Nov 2015 22:32:11 +0000:

Of course it applies here. Read again and keep reading until you
understand it.

But if you're saying the 40W is actually 40VA, where is the math
that backs that up?

All "my" math (given only the printed numbers), come up with
34 Watts (DC) output with about 80VA (RMS) input.

Nothing is even close to 40W or 40VA.

If you understand inductive or capacitive reactance in AC circuit.
Most load in AC power has inductive reactance meaning voltage leads
current by certain amount depending on how reactive it is. The more
phase angle, less power factor losing power as wasted(non energy
producing) Power factor is expressed as Cosine Phi So when the angle
difference is zero PF factor is 1 which never will be. Less than one,
VA and W=V*I are not equal. I just explained it in layman talk. Draw
a full Sine wave one for voltage and one for current. In this case
voltage wave leads the current wave by few degrees. So both waves does
not super impose. The difference in phase angle expressed in Cosine is
PF. In the case of capacitive reactance current leads voltage. You
should know conjugatory number? +jR is inductive reactance, -jR is
capacitive reactance. AC circuit impedance Z is root mean square of DC
resistive value plus +/-jR Still Ohm's law like in DC cibut reactance is
additional parameter. I hope I made some sense. If I have blackboard
I could show you with graphics.....

+jR is 2*pi*f*L (f in Hertz, L in Henry) -jR is inversed 1/2*pi*f*C
(C in Farad) Opposite of Impedance Z is called Admittance Y=1/Z

If there is step down transformer involved power can incur some loss due
to poor material like heating up the core iron Not only PF is an issue.
Any power supply produce heat(lost energy lowering effciency)
For an example look at the power supply for desk top or laptop PCs.
Good ones have higher efficiency as well as producing clean very
stable outputs. You get what you pay for applies here too, LOL!