Here's part of an interesting article that was published in the fall 2000 issue of 'The Audio Critic'. It puts a different spin on line conditioning:
Just about all that needs to be said on this subject has been said by Bryston in
their owner's manuals:
"All Bryston amplifiers contain high-quality, dedicated circuitry in the power supplies to reject RF, line spikes and other power-line problems. Bryston power amplifiers do not require specialized power line conditioners. Plug the amplifier directly into its own wall socket."
What they don't say is that the same is true, more or less, of all well-designed
amplifiers. They may not all be the Brystons' equal in regulation and PSRR, but
if they are any good they can be plugged directly into a wall socket. If you can afford a fancy power conditioner you can also afford a well-designed amplifier, in
which case you don't need the fancy power conditioner. It will do absolutely
nothing for you.