Power conditioner products?

I have a Russ Andrews The Silencer

 http://www.russandrews.com/product.asp?lookup=1&region=UK&currency=GBP&pf_id=1403&customer_id=PAA2250062410489RKWTONLKWYFGIHQX

It has been plugged into various hifis and TVs in various houses. It has varied in its effect depending on how 'noisy' the mains has been at each house. I presently have it plugged into the first socket on a mains extension. Without it I hear background hiss through my headphones, with it the hiss has virtually disappeared. 

When I changed from a Dell to a Sony laptop which is plugged into another mains extension, I noticed that the background hiss increased. The laptop was putting more 'noise' back into the mains. So I got a Tacima plug in conditioner (not the mains extension so many use) and again the hiss went away.

I highly recommend the Audience Adept Response conditioners. The single outlet Ar1p models are often on Audiogon for under $350. Just add a half decent power strip (no surge protection, the Audience takes care of all that) and you've got system wide conditioning that will beat up other conditioners at $1000+. In my opinion, Audience > Shunyata and most others. The AR-T models are pretty much unbeatable, with perhaps only the top Running Springs and a few others even in the same ballpark. 

I would avoid anything that limits current, they almost always are worse than running no conditioner.

I use balanced power products from BPT (do a search on Balanced Power Technologies). They have multiple levels of products including rather higher-end power strips. Similarly, check out Equi=Tech, the originator of the balanced power NEC spec for the US.