Understand that all modern electronics have well regulated power supplies as part of their design. The one exception might be some android boxes that use "wall worts" or simple power adapters. Some of those can benefit from a better power adapter that uses a switching power supply. TVs and projectors will not have that issue and neither will receivers or amplifiers. Power conditioning will have no effect on video images.
When is a power conditioner appropriate? If you live in an area with unstable electricity supply and are susceptible to brown outs (low voltages) or spikes (high voltages) or lightning strikes. A power conditioner (and not just a simple spike protector) will condition the source voltage to provide a constant 120V, making up for low voltages and clipping spikes. This will not improve image quality because the internal circuitry in the TV already uses a regulated power supply that guarantees a fixed DC voltage. It will however protect your equipment from damage. This can be especially true for areas where the power goes off completely for a second and then back on again. The equipment will run off of the power conditioner's battery and not even know that an outage occurred.
You do not need to spend huge dollars on this. A computer UPS (uninterruptible power supply) from makers like APC and Tripp Lite work just fine. You just need to match the power rating to your equipment. If you get something in a rack mount form or audio style case from Furman or Eaton what you are paying for is aesthetics and pretty packaging. You can spend thousands on "audiophile" conditioners but as far as your equipment goes a UPS from APC for a few hundred dollars works just as well but won't look as nice.
This only works for units that have an internal battery and can supply full AC voltage when the power goes out. Units without a battery can only provide surge (spike) protection. For surge protection, most people are now moving to whole home surge protectors which get installed into your electrical panel and protect the entire home.