Tony Hwang wrote, on Mon, 30 Nov 2015 17:12:02 -0700:

What is power factor? USB works on DC current.

I don't fully understand the power factor but it only applies,
AFAIK, to the AC input voltage time current.

Even then, I think it only applies when you add multiple AC
wattages up.

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.

At least that's how I understood it after reading about it,
but, I don't think the power factor applies here, as you said, b
because we only care about the output power, which is DC.