I've got the Summertime Blues. Power conditioner necessary?

udog -- I have my 3 stand-alone mid-fi systems connected through Furman PL-PLUS DMC Power Conditioners.  The unit provides a reasonable degree of power conditioning and circuit protection at a reasonable cost.  Living in quickly growing area of South Carolina, I encounter a double-whammy of thunder and lightning storms and significant fluctuations in voltage.  Due to the massive residential, industrial, and infrastructural development in the area, I have voltage fluctuations from 113 to 125.  The good news is that my average is 121v and I can monitor near brown-out and surge levels.  Consumer grade surge "protectors" used in the past resulted in severely damaged audio equipment, attributable to both a direct lightning hit to my home and the concussion of thunderclaps.  I now have an all-home power protection system in conjunction with the Furmans.  And, for good measure, I shut down and unplug the units when the forecast calls for severe weather.  NOTE: I have acquired the units at 15-20% off list price and free shipping at Musicians Friend, which also has an excellent hands-on article on the unit written by Darius Van Rheul.       

A friend in an apartment building had a similar problem. I gave him a large Constant Voltage Transformer that I had purchased as surplus for $60. It solved his brownout problems cheaply.

At my own home, I had the electric company increase my home service from 100 amp to 200 amp, then had new dedicated power lines run from the service box just for my system.
Good Luck

My system has all digital sources, and I've found that the better the quality the AC power is, the DACs extract more detail with less distortion.

I used to have a very nice, modestly-priced Furman unit.  When I upgraded to a PS Audio P10 Power Plant, my DAC immediately sounded better.  I recently took advantage of an upgrade, trading in my P10 for a P15, and immediately, both of my DACs provided better bass, more detail and better soundstage.

 I use Chang LightSpeed power line filters and they work great! They have digital and analog AC connections.

Found them used for $400 to $500 and use them on my main audio system and home theater.

Also protect from lightning strikes.

For several years I lived in an area that’s electric power was supplied with large diesel generators, bad wires and noisy transformers. Running my equipment through a APC power conditioner, on it’s own circuit, helped clean most of the noise and stabilize the erratic voltage drops and surges.

While I agree that a good power conditioner can help and does add a level of protection, there are many myths and an abundance of false info. regarding your power supply.

As cleeds pointed out - you Can Not put a sub panel on a separate ground; all grounds must be connected to the common ground at the main.

You can eliminate ground noise by connecting to one end or the other of the circuit panel. No - all circuits are connected together on a common ground. The best solution, if you can - eliminate the source of noise - usually an appliance or component with a bad transformer, rectifier or ballast
.
A dedicated 20A circuit with 10awg wire to supply your audio components. Really? With the exception of a very few high currant power amps - what audio components come with, or are required to have a 20A cord or, in any way, require or would benefit from a 20A circuit with a 10awg supply line? They don’t!

Have the power company provide you with a separate power supply for your stereo system? Power companies supply power to your main; the supply main, the primary panel, and sub panels are the owners responsibility and are required to meet the NEC. To get a separate service is very expensive and is only practical if you are operating a commercial business, that needs to be kept separate from your home, or have a shop operation requiring large amounts of additional power.

Not trying to be snide, just saying - some of the ideas thrown out here are impractical, improper or, in general, make 0 difference in the sound or performance of one’s audio system....Jim