power cable factory versus brand name gauges

Hi I have a few 12 gauge power cables from amplifiers that i have bought and sell. They all seem to be built the same, very thick and hard to twist or bend. All are built as 3 wires inside another insulation. I have cut open one of them, all the three wires are stranded and seem to be copper, at least the copper look very shiny instead of oxidized which is good.
I have finally started buying some brand name cables like Nordost Shiva and Vishnu. However they are all of smaller strand wires, namely, built as 16 gauge wires.
I guess I need a refresher course in electricity, why would these 16 gauges be better than the 12 gauges wires i presently have? Would the stranded 12 gauge present a lower resistance and capacitance? What is this argument that a wire has 90% transmitting at speed of light? I am a bit confused as people say they hear a difference but what would make the difference?
Would buying a UPS with true sinusoidal wave output be better than buying a power conditioner? Would this purchase be better than buying power cables?
>Would buying a UPS with true sinusoidal wave output be >better than buying a power conditioner? Would this >purchase be better than buying power cables?

there are many poor components in those "true sinusoidal units" , and they bring so much noise in to the sound system, that I doubt anyone reached any truly positive results..

as for me.. I have a couple of brand name cables right now laying arround my system from kimber pk10,pk14, nordost shiva, and others.. not the most expensive cords, though.. they do bring some changes to the sound, BUT I still keep those ugly, thin stock cords pluged in. Believe it or not, they also have "own signature sound" and it fits my system better. I notice more natural inner details of voices and better dynamics with stock marantz 2x16 AWG cord than with any other cable mentioned. But its ugly compared to well made "brand name" cords, I admit !

Your results mirror those of mine. I know that my equipment was voiced using the stock pc`s not the `high end` power cord. I have spoke with the manufacturers of my system and they recommended the stock pc. The `own signature sound` is how the equipment was voiced. Like you, my Marantz sounds sounds great with it`s stock pc.
thanks for your contribution to your experieces
we have talked about these power cables on amps/preamps
would the same hold true for source or turntables?