HiFi vs Cheaper Power Conditioners; What's the difference?

I had a quick question follow along this. Can someone let me know the difference between power conditioners like the furman 15 pf i (which I can get for a couple hundred dollars) and their reference line or ps audio p5/p10 or audioquest niagra (which will be in the thousands of dollars)? I just was hoping to get some clarity on why one is so much more and what it does so differently. Thanks.