Power cord that improve the soundstage the most?

Here's what I think people should do (in order of importance):

1. Put in dedicated circuits.

If that's not possible then:

1a. Put in a power regenerator (NOT a conditioner!)

2. Get the best PC you can afford that has:
10 AWG conductors and,
A floating shield.

Get one for your amp and another for the regenerator if you have one.

3. Spend the money you budgeted for PCs for your front end stuff on a balanced power unit instead, and plug all your front end stuff into it. If you have a regenerator, plug the balanced power unit into it. If you have dedicated circuits, plug it into one that's reserved for your front end gear.

If you want to buy one more PC, you could get another 10AWG shielded for your DAC or CDP. Other than that, I'd leave everything stock.
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It is inconceivable to me that $3,500 spent on a component upgrade won't do more to improve your system than a $3,500 power cord.

For a system in the + $200,000 range then maybe, but spending that much for a power cord, in most situations, is sheer insanity.

Take a deep breath and come back down to reality.

Herman, I don't think they sell a lot of $3500 PCs. I use PAD Dominus. They're expensive (but can be had for $900 used) and so are any of the really good ones like Virtual Dynamics, Aural Symphonics, etc. The reason they're expensive is not hype (for the well respected ones) It's because they have to source small quantities of expensive alloys and other materials, perform additional processing like cryo treatment, and hand-build the product one at a time. All this gives them just a little extra performance in the 'energy transfer' department. Not enough IMO to justify all the extra expense, unless you own a highly resolving system -- in which case you WILL hear the difference.
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I have had good luck with the Pure Note Enhanced Paragon. It opens up the soundfield and lifts all the haze. A bit cheaper at 300 bux.

Shunyata, Shunyata, Shunyata. The more you have in your system, the more the effect compounds. Not cheap by any stretch though.

Some of the cables are component specific; for example, diamondback and amps are a mismatch while the diamondback is great with digital. I would recommend a couple Taipan Helix cables to start with, well worth the investment imo.