Certainly has made a difference for me on all equipment.
You don't realize that there can be blacker backgrounds until you get it from an upgraded PC.
Have one on my integrated amp (MF A300); and on my sources (Pioneer Elite DVD/CD, Cary 308).
I think it may depend on the actual construction of the power supplies and power delivery of each component as far as the amount of improvement, but I would recommend using one on all of your equipment except a subwoofer which probably does not need it.
No need to spend huge dollars as the upgrade from stock 18ga cords is significant usually with any aftermarket cord.
I started out using DIY 14ga Volex PC's that cost me about 10 bucks to make. Nice improvement all around.
I then splurged and switched out to Ven Haus power cords for everything which are less than 100$ a cord pre made (or you can do DIY with his materials) and they really allow the equipment to sound their best IMHO.
I am sure there may be are better cords than what I have, but for the money the VH cords are a great value.