what does a power conditioner really do?

Ive used a lot of different products in this category over the years, Tara Labs Power Screens were the best but they're NLA and hard to find used.  

I currently run a PS Audio P10 and it works great.  Solves several power issues I have in my state and provides some excellent diagnostics realtime and post event.  I bought mine new at 50% off retail from an authorized dealer...