PCOCC single crystal construction and the Skin effect
It’s important to think of the power cable as it relates to the current needs of the amplifier.
The audio being played back places requirements on the amp and thus, a load on the power cable’s ability to allow current to flow from the wall.
As the current flows through the cable the electrons will begin to flow around the surface of the conductor.
This is called the skin effect.
Skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is largest near the surface of the conductor and decreases with greater depths in the conductor.
https://en.wikipedia.org/wiki/Skin_effect
The skin effect changes with surface area based on frequency.
The square conductors in the AC 12 cable allow for higher surface area and take into account a broader range of this effect.
http://www.psaudio.com/products/ac-power-cable/#tab-ac12
The skin effect does not come into play at lower frequencies of the audio spectrum.
Different shapes and geometries of the copper cables represent different frequencies and rates at which the audio product can pull current.
The construction of the cables allows for changing frequencies at which current is being pulled from the wall by the amp or DAC.
With regard to the PCOCC single crystal construction, crystal copper lowers the resistance and allows current to flow more freely.
This superior grade of copper combined with the shape of the conductor makes for an audio power cable specifically designed to allow for maximum audio performance.
This is a paper on the AC series that talks a little more in depth about the cable:
http://www.musicdirect.com/documents/pdf/APSPWAC.pdf