Longer Power Cords Sound better?

In a word; NO.
If your PC sounds better in a longer length, then you've got the 'wrong' pc. Of course, by wrong, I mean 'less than optimal', not 'horribly awful'.
I've listened to pc's in roughly .5awg increments between 9awg and 13awg, and in .5 ft increments between 3ft and 8ft (in gauges 10-12).
Yes, I'm that obsessive.
And when you find the 'right' gauge and length, that's when you discover just what your gear is capable of.

...13, 14???

Gunbei, Sonic_genius :nice maturity levels...when you grow up, get educated, and know how to respond like mature adults...yes Romy the Cat says it well....there are AUDIO MORONS on audiogon

I have herd that Shunyata was once commissioned a 30 ft length of Anaconda Alpha (original series) with amazing results. Unfortunately I have this info only 3rd hand with no additional detail, except for the resulting sound being reportedly superior to that of the standard 6ft length.

Longer PCs sounding better is an urban legend. They abound in this hobby`s gullibility quotient.

Cables have their rated electrical parameters specified per unit length, typically per foot or meter. As such, their level of capacitance (for example) will increase linearly as the length of the cable increases. Therefore depending upon a cable's specific design parameters, different lengths can offer some significant differences in apparent sound quality. In some systems and applications higher capacitance in a power cable may be a desirable attribute, while in other scenarios it may not. The same applies to a cable's rated inductance and resistance. YMMV applies well with high end audio cabling solutions.