Power Conditioners

Not sure if I placed it in the correct topic but here goes. I was just wondering how power conditioners work, as I want to buy one. There are conditioners with only filtered inputs and conditioners with some filtered inputs and some unfiltered. I believe the unfiltered ones are for analogue devices. But why should these go into the unfiltered part? If I buy a power conditioner for example with only filtered inputs, will I not be able to put my class A amp in? Or will it have a negative effect?