Least expensive plug-in power conditioner that works

Tripp Lite makes a series of voltage regulator, noise filter, and surge protector. $115-300 on the big A. They're especially designed for computer rigs. 

@mashif 

That model Tripp Lite is not a power conditioner.  

@lonemountain

I never used the term "power conditioner" although that is the way Tripp Lite describes it. I described exactly what it does. Argue with Tripp Lite. 

No disrespect meant to you, but this is exactly what I was talking about- tremendous amount of disinformation in this product category from manufacturers and their marketing departments (or lack thereof).  A power conditioner needs a big transformer to do "power conditioning" and isolate the inside power from outside power.  Tripp Lite does make one but there are multiple players on this category (but mostly industrial).  Most of these other devices are fixes for other problems like surges, noise put on the internal lines by a noisy power supply from something plugged in to the internal power ( a big issue in studios) and voltage regulation (can be a big issue to keep power stable at 115V /120V in some parts of the country).