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?
To anyone who doubts the efficacy of a good power conditioner because they haven't heard a difference, I'd like to know if your gear has lights, meters or displays that can be turned off. 

If so, try turning them off to see if you can hear a difference. If you can't, then it's you and not the conditioner, or, your system is simply not resolving enough.

I say this because when I first got my Marantz Reference gear (integrated and SACD player), I tired it with the display on or off and couldn't hear a difference. That was before I got my Niagara 1200 and the Isoacoustic Oreas. On a lark, I tried it again and the difference was big enough to make me reconsider a lot of things. 

There's now so much more air, separation, detail and nuances laid bare that those dirty LED displays were injecting noise back into the gear and superimposing itself on the music, blurring things more than just a little.
The line noise was so dirty that it helped cover the negative contributions of the LEDs. 

Before my getting the Niagara 1200, I thought LEDs and displays had no real effect at all.

All the best,

the answer is yes - others heard the difference easily. I have had a number of conditioners in the past.  None were cheap and none really made a sizable difference, but I wanted to protect gear.  My dealer suggested I audition a Niagara 5000. The difference was plainly and immediately audible. I didn’t have to squint and ask myself what was I hearing.  My reaction about 5 seconds into the audition was “crap now I’ll be spending $4k”.  Obviously, every situation is different such as quality of power coming into the house and the gear you’re using, so YMMV.  For what it’s worth, my local dealer told me that every customer who’s auditioned the Niagara at home has purchased one.  I was sincerely hoping to prove him wrong. 
For my "all digital sources" system, each time I've upgrade the power conditioner, the performance of my DACs improved.
Does anyone use Equitech 2Q to any benefit?
I use SurgeX for all my network stuff, modem, router, NAS and a separate one for cable box, TV, sound bar.

I have dedicated 20amp circuits in another room for my main system, and use a Shunyata Denali 6000S/ V.2 for everything except subwoofer which is on its own circuit and it has a Shunyata Venom Defender on it. And of course if I’m getting a huge massive lightning storm I just disconnect everything.