I've only had 3 power conditioner over the years. I started out with an entry level Belkin PureAv. I couldn't hear a difference with the gear I had at that time. I liked it because of the protection it provided. Next was the PS Audio Quintet. I had it for about a year before recently selling it. I never really had a strong stand about it. There were times when I thought it decreased dynamics, other times I felt it was transparent and other times I couldn't tell. I wouldn't say I every heard an "improvement". Maybe that's because my power is fairly clean? or system synergy? Not sure.
Awhile back Dan Modwright had recommended to me getting a Running Springs power conditioner. He said that it didn't limit power and made his gear sound their best. I finally bought a Running Springs Haley last week- got it used from Audio Circle forum. It is Passive and has 6 outlets and was enough for all my audio gear plus my Panasonic Plasma.
Right in the first moment of hearing it I could tell there was something very different about what I was hearing. It was not subtle. I wasn't expecting that considering my past experience with power conditioners. It took me a couple days to really get a grip on what I was hearing. Most apparent was that there was more weight. There was also in increase in separation. Both the top and bottom end got extended. In fact, there was such in increase in low bass that I hardly use my sub now.
Now for the first time, I can say that when I listen to my rig, it blows me away every time I listen. I'm thinking that the Haley has allowed all the other components to shine closer to their potential. With the level of realism I'm hearing, it's like all my cd's got upgraded to SACD status. When I listen, I have this big grin on my face that is stuck on there.
A couple things to note: Last month I upgraded my AC receptacle from stock to a Porter Port which I also found to be a Significant upgrade. I had no idea how much my cheapo receptacle was limiting the music. This upgrade is a MUST for audiophiles.
Lastly, there's two versions of the Haley. I got the older version, which sells used for $700-$900. The newer version has a couple upgrades that further improves the base model. New this costs $1900 and I've seen a used one for $1000. You could also send in your old model to have it upgraded to the newer model for $300 I think.