Are manufacturer AC cables good enough?

As long as you're willing to settle for, "good enough".............

A, "THEORY" has never proven anything, either.      That's ALL the, "evidence"  naysayers have ever offered, in their, "scientific" pontifications.       No one will ever know, whether a component change (whatever the component) makes a change, in their system/to their ears, without actually trying it, which (whether your ilk recognizes it or not), constitutes an experiment.   

Too lazy to copy/paste something, in your search bar?     Typical naysayer, to ignore something so simple!      If he ever owned a sound system, I have no doubt, he’d have EXPERIMENTED with it!       Your ilk is an embarrassment, to the scientific community, not to mention: a waste of keystrokes. https://www.brainyquote.com/quotes/richard_p_feynman_160383

The hypothesis is (whatever the particular wire, tweak, etc); that a change (good or bad) can be heard.     If one desires to apply, "science", to an agenda, regarding their listening enjoyment; experimentation is an absolute requirement.     iow: One must actually TRY, whatever’s being discussed, with their own ears, in their own system.      The electrical/electronic variables, as well as biases and/or aural acuity, are too myriad to calculate.      As one notable Physicist, theorist and Nobel Laureate (popular, for his lectures on QED) is usually quoted, " It doesn’t matter how beautiful your theory is, it doesn’t matter how smart you are.    If it doesn’t agree with experiment, it’s wrong."       THAT’S, "logic".

Never said gravity couldn't be explained.     The amount of gravity, throughout this universe, has not yet been explained.      I cited a number of the theoretical attempts at an explanation.     Jones brought up Einstein's Cosmological Constant.     I mentioned it sought to account for the amount of gravity, throughout this universe.      He added that, in his Math, believing in a stationary universe, in keeping with that time's understanding of Physics.    Anyone, with even a minimal grasp of Einstein's General Relativity, would have understood that point.          

Again;  The hypothesis is (whatever the particular wire, tweak, etc); that a change (good or bad) can be heard.        The naysayers propose (perhaps, project), that, "audiophiles" are too ignorant, inept or deaf, to make a change, in their systems, listen to it and determine if it (whatever it is) makes enough difference, to them, to purchase (a simple experiment).       Without a knowledge of the root, which births such hubris, one could almost get offended.      ie (the root):     https://www.britannica.com/science/Dunning-Kruger-effect

Munching a good Filet Mignon, makes everything better, doesn’t it?    Of course: many appetites could be satisfied with a filet from Costco, which would, "do the job" (like a spare computer cord).     That’s up to no one’s palate, but the muncher’s.    For other appetites (biases): there’s Wagyu Beef Filet Mignon (not American, but- the real deal, from Miyazaki, Japan).    As I mentioned, in my first response to the OP/this thread: As long as you’re willing to settle for, "good enough"........

But....the Doctor said they would help!

"Synergistic Research also claims to do exhaustive double blind testing, but again, never publishes anything, nor allows independent verification."         Excuse me? Synergistic offers a 30 day satisfaction guarantee, on virtually everything it sells.       That should be sufficient time, for even the most obtuse, to discern whether a component change results in an audible difference, in their own system.      Ever been to an electronics trade show?    Mr Denney goes to lots of them, around the globe, at which he demos his wares, openly, proudly and with great success.     ie: https://www.synergisticresearch.com/best-of-show-awards-2015-all-major-shows/

The Farce is strong, with these two.

         "But has never done double blind with any verification or validation."         Verify/validate that statement, somehow, please!

I AM (thanks)!

@heaudio-      So; you, "call them out" with ZERO verification/validation, of your statements (iow, "TRUST ME")?

I didn’t make your totally UNSUBSTANTIATED statements!     It’s your ilk, that incessantly demands, "EVIDENCE."    You’ve made a number of claims.     Now- back them up, with something!

@turnedown-      Yeah, that settles it!

@jl35- Your biggest mistake, was to have actually tried some better cables and cords.     Now: you need to sell those and forget everything you think you heard, because: your deceitful/malfunctioning ears and brain, obviously misled you.     TRUST ME (snort of derision)!

@jl35 -      " ....the only testing that matters is the testing you do at home in your own system... and we buy with return privileges so there’s no bias to "pretend"...      There you go again: being logical and making sense!     How dare you (and/or, cleeds)?

"I don’t see much evidence that there are many here who are in your #3 group.    That’s because many of those who would pretend to belong to that group either dismiss mountains of evidence with a wave of the hand or - just as often - simply pretend that the evidence doesn’t exist."      Empty vessels make the most noise!     The source of their hubris: https://code.tutsplus.com/articles/do-you-suffer-from-the-dunning-kruger-effect--net-22227      Those with even a modicum of scientific understanding, realize how much remains, to be explored and proven.