Power cables, I need help

I have finally got all the components that make very good music in my system! My last tweek is power cables & maybe a line conditioner. I have read here on audiogon where some use p/c's only on certain components and some suggest plugging them only into the wall outlet. I have also read sometimes a/c conditioners do more harm than good. I have mono block tube amps and a tube preamp. I would be willing to spend $1,000 - $2,000 new or used, what should I be looking for? & is there a component that works better with a power cord?

Thanks, Bob