Dirty household current can certainly adversely effect sound quality, usually dramatically so… Think hum, but that could also be from a ground loop and best eliminated by an isolation transformer (Hum?…  Maybe it’s just a ground loop).  Power conditioning should be redundant to the power supplies provided in your components, which makes claims of better sound quality from overpriced, dedicated power conditioners (some cost thousands of dollars) illegitimate.

Remember, that if you are going for audiophile sound quality, then you are purchasing components that have already gone to great lengths to optimize their power supplies to that end.  Then of course really high end audio provides separate power supplies for each channel.

Such high end audio manufacturers are assuming you are running off household power (including the incumbent flaws there-in), that is what their equipment is designed for.  If you think you need elaborate power conditioning units to improve sound quality, then I would re-think the components you are purchasing.

Rather than “second guess” the adequacy of the power supply in your components (you’ve already chosen ones that are exemplary in that department, right?), money spent on the purchase of elaborate power conditioning units for your high-end audio components could be better spent elsewhere, such as high quality recordings.

That said, a power conditioner can serve a simple but indispensable task, that of surge protection from lighting strikes or other aberrations from your local electric provider.  Consider it a sacrificial part of your audio chain, rather than one that is essential to audio quality.  If lightening strikes and takes out your $100 power conditioner and saves thousands of dollars in high end components , it will be the best dollars ever spent.

Oh… and about “high end” power cords?  Same comments as on power conditioners.  Sure you can spend up to $2K and go solid silver or something ridiculous like that, but why on earth would you.  Any manufacturer of high end audio gear will have considered the quality of the power cord they have provided and even designed it specifically for the power supply of that component.  So not only are you “second guessing” their choice, you are also superseding their design and quite possibly introducing mis-matched wiring.  Of course this would mean that not only have dollars spent on an “upgraded” power cord been wasted, they have actually been spent to degregate the quality of the power supply in the component they are used with.