The one I have at work is transformer based. I hear it click into service when the HVAC kicks on. But as John was saying the power supplies in most equipment have their own transformers, and are designed to clean up the power before turning it to DC.
Without batteries and full sinusoidal regeneration ($$$) I don't see any inline conditioner really offering anything beyond what's contained within the gear. I put the one on my PC at work, because we had it, and I wanted to see if it would do anything--it clicks. If you can get one cheap enough, maybe you'll have the same use. But remember what I pointed out, they can't provide the same current levels as the straight mains, so don't use any high-draw gear on it.
