Wouldn't we all like to know.
Tvad is right, but before you start your research, here's a guide to the main groups:
Power Conditioners: A little like hair conditioners. Smooth things out (filters), repel dirt (EMI and RFI) and provide anti-static protection (voltage spikes.) They can't provide voltage or AC frequency (60 cycle) accuracy. And they provide what attributes they do provide, some think, at the expense of sonics.
Power Regenerators: These devices do all the things that conditioners do, but instead of employing passive filtration, they do it using active electronic circuitry such as signal generators, linear amplifiers and feedback loops to regulate the wallpower. What you get is what (in a perfect world) would/should come out of the wall.
Balanced Power Units: These units have been in use for years in studios but only UL Approved for consumer use for about 12 years or so. They reconfigure the 120V-to-neutral plus ground conventional power layout, into 60V-to-neutral-to-60V. Thus creating a noise-free (self cancelling) conductor layout just like XLR balanced interconnects do. Primarily used with lower powered more sensitive front-end (source) stuff, but can be used with amplifiers too. Excellent when combined with a regenerator unit. For more info on the hows and whys of balanced power, go to the Equi=Tech website at: www.equitech.com
Your own equipment may be the worst offender ... in a sense "You've hired your own Assasin"
Dacs, Switching power supplies, Oscilllating clocks, Diodes, and more,(any thing that switches on, and off at a high rate) can add noise back into your system's power supply.
Look for a Power Conditioner that filters on the back side or is Bi-Directional
My combination consists of an Exact Power EP15 to generate square sign waves, and Foundation Research's (LC1) to filter Bi-Directionally
There are too many variants to make for easy categorization and too little information disclosed about how individual units work. Thus, Nsgarch's descriptions are fine but there are other variation and permutations (automatic voltage regulation, battery-power, etc).
The bottom line, for me, is to determine if you have a problem that needs solving and then find the solution. Adding gadgets based on someone's encomium won't do it.
Gossip says Monster Cable is changing it's lineup soon.
Plenty of dumping of Monster hi-end conditioners going on.
I could have gotten a 7000 for $600 new, or a voltage thingy for $800. The whisper is they are being hammered by better sounding and cheaper stuff from other companies and need to revamp the line or die.
Whether this is rally true I do not know.
But it feels right to spread about a company that has gotten to self-important ("monster" lawsuits) for it's own good.
Go to ExactPower's website (www.exactpower.com) for details and an animation showing Exactly what it does to a distorted sine wave.
I live in an apartment, and run my whole system off a single dedicated 20A circuit. I have an ExactPower SP-15A (balanced power unit) daisy-chained off an ExactPower EP-15A (power regenerator). All front end stuff is plugged into the SP-15A (balanced power unit) which, as I said, gets its power from the EP-15A, along with the amp, speakers (stats) and sub.
With everything turned on, the entire system only draws 450 Watts at medium volume. With the volume control turned up to med-hi with no signal (on the phono input,) the system noise floor is about the same as an unoccupied chair.
I had one installed since I put together my Audio system and that was 3 years ago. Just started getting back into Vinyl just last year. Anyway to make a story short.... had to move audio furnitures around 2 months ago and disconnected my Power conditioner on my front ends (connected directly to wall outlet)....and WALLAHHHH.. my system sounded so good (PRAT..galore) I cannot believe my EARS. Everything you threw at it-- CD, Vinyl, Ipod..damm sounded soooo good. Bass was so pronounce and very palpable..with authority.. The sound experience was like listening to live performance 10 ft away....(to me anyway):^)).. So now I have all my electronics connected directly to 1 dedicated 20A circuit. Felt like I was robbed of good quality listening for a long time...just to share my experience.