A correction on power factor. Power factor has to do with the current and voltage fromthe wall being 'in-phase' with each other. In high power applications with an inductive load (like a toroidal transformer) the current and voltage become out of phase with each other thereby reducing the actual power available. For example (as RPL correctly points out) when you draw 10A at 120V from the wall, you would expect you get the full 1200W. In reality you get 1200VA and depending on the power factor, say .7, you would only get 70% of that or 840 Watts to use in your amplifier. Its a big waste.

The issue regarding the diodes is efficiency, not power factor, but the end result is the same, less power.

But in my experience with power factor correctors is they add distortion to the line, not reduce it. They try to draw current in phase with the volatge, in doing so causing current spikes. They do however correct the phase issue and get the power factor closer to 1.
The other piece of this puzzle is the type of supply that is converting the AC to DC. Here RPL is talking about a linear supply with series diodes, which is very inefficient in terms of converting power. A switching supply is much more efficient, but at the expense of noise.
My point of all this is there is much more to getting power, more importantly clean power, than just power factor.