Are manufacturer AC cables good enough?

PLACEBO EFFECT:  The more you spend, the better it sounds.  We trust the designers and manufacturers to make really good equipment.  Would they really sell something as cheap to make as a power cord if it made their great design sound worse?  It takes three months to break in.  NO!  It takes as long as three months for your credit card to automatically refuse a refund.  Dealers like profit and reason for you to keep visiting.   An expensive power cord is about as effective as the Scotch Guard on my Tacoma seats that I was charged for.  The unused can of Scotch Guard was in a storage compartment, to be found months later.  If an amp has a crappy power cord, what other cheapness is in the unit?

I went to such a test.  About 50% picked the more expemsiver power cord.  We did find a difference in interconnects, but only the very cheapest were picked very often as the worse of a choice.  The others were about 50-50, with mostly guessing.  There was never a consensus, except for the decades old, cheapest crap from Radio Shack.  Basically, any cord with oxygen free copper was deemed somewhat better, but that could simply mean they were put together better, or had better insulation, etc.  One exception:  If your power cord runs parallel to your interconnects, or even crosses them, better insulation/grounding might help. 

The tweaky magic stuff allows you to share the experience of visiting your dealer to talk about your hobby.  It makes you happier, so you believe it works. This is a great marketing plan, because every time you visit the store, is a selling opportunity for new equipment.. 

When a builder stakes his reputation on his design, he will use a good cable.  When a product is subcontracted out, NO!  Jame Bongiorno, of GAS/Ampzilla fame,  was supposed to be a great designer, but compared to similar Julius Siksnius designed and built Audire equipment, it was junk.  The difference:  James had his stuff made by bidders; Julius built his own factory..