12 AWG Mains Power Cable From Wall To Power Conditioner Sufficient?

I prefer a quality insulated cable. I couldn't hurt. Just don't spend a ridiculous amount. 

Yes of course as said before if it’s on a 20 amp breaker, it’s the same  gauge as what’s in your wall. And sound quality has absolutely nothing to do with that at this point !!

Gague isn't the final defining factor one power carrying ability. Look to your manufacturer for Amp rating and go from there. Depending on what kind of cooper, plated or not, how many strands, how the strands are configured Type and grade of shieling all play a part in they power cables, I would suggest that you decide how many amp you commonly need to provide and  have a cable rated in excess of that. If yo are using a standard 15 amp wall socket then I would want a Distribution box capable of 20+ amp and the power cord possibly capable if 25 amps should be sufficient. Like with your power amp overhead can make or break a sound. The same goes true for power handling capacity in you  'line-in' side.

How much power is the subwoofer rated at?

@ryder - as someone above posted - the Gauge of the power cable is not the full story

• The wire in the wall is genrally solid wire
  • it is capable of delivernig better/cleaner power than a normal power cable
• Power cables generally use a stranded wire to maintain flexibility
  • stranded wire cannot carry as much current as a solid wire

Some power cables use a solid wire or 3-4 solid insulatied wires

• these generally perform better than most other power cables.

But that is only a small part of the story - take a look at this thread for a more detailed explanation

What Makes A Good Cable

Hope that helps - Steve