Chad, ded. lines are always a good thing, cetainly one of the most cost-effective improvements one can make. But there are two big things they won't fix:
1. They won't improve the AC your utility company is sending you in terms of inaccurate sine waves and fluctuating 120 voltage. And,
2. They can't eliminate noise that gets into the powerline before it reaches your house.
And to Matchstick, for a long time conditioners were all we had. They do their thing using big filtering devices which, by their nature, limit rapid energy transfer between the powerline and your components. This is a problem particularly for amplifiers (which always will suffer a reduction in dynamics) and to some degree to DACs, for reasons I don't yet understand. But used elsewhere, they can help, there's no doubt about that. It's how they do it that's the problem.
Further, conditioners can do absolutely nothing about #1. above. However, regenerators can fix both #1. and #2., and do so without limiting dynamics the way conditioners do, since they eliminate noise through a technique that doesn't choke energy transfer.
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