I need help choosing a power conditioner.

I am interested in adding an inexpensive power line conditioner to a second system that I have in a spare bedroom. Stereo only, no video. Budget is $150.00 used and some recommended contenders are, API Power Pack 2, Adcom Ace 515, one of the various Monsters, 2500 maybe. Degree of system improvement is the only criteria and I would appreciate input from respondants with experience with at lease two units so that I can get a contrast. Please feel free to add other models into the mix. Your knowledge and guidance are greatly appreciated.
$150 is a hard call, adcom seems to be popular, you might be able to score a good deal on a used monster 3500. very nice unit workrd great for the bucks!
Out of the ones listed definitely the Audio Power Pack II. It does the best job in my opinion and has a detachable power cord, so you can tweek that system further with a better cord. They do give you a good fat one with the unit new.

The Monster is OK and will do a decent job. It is well like by many for the cost.

I would avoid the Adcom. A few I heard actually added noise to the system.

Another nice unit in that price range is the Vansevers Super Companion.

You can't beat the Monster Power 3500 for the money
Viridian, Check the Dave Magnan home-brew recipes for power conditioning. He gives simple solutions for little money if you are a little handy with a soldering iron.
At that price break, I would forego any power conditioner as it may offer little or no benefit and may actually worsen the sonics. If you bought a $300 lc for $150, then that could be better.

And by all means try to borrow a high quality line conditioner for a/b comparisons with the inexpensive lc. That way, you can be assured exactly what you're getting or not getting with the inexpensive lc.
I would also consider getting a couple Blue Circle Noisehounds $100 each (one is OK). Nothing else at that price will clean power as well.
After my house being hit by lightning, through my satelite, I would recomend some type of protection no matter what it cost. My damage was over 10k in electronics (stereo & computer) luckily no fire. I use Panamax products currently but I have read great things about some of the Monster products. Conditioning is included as a bonus in most of the more inexpensive units. I use a Panamax 1000 that would fall in your price range, It has been discontinued "I think" but there are still plenty available. Give Panamax a look IMO they are comparable to what you have listed.
I've spent years trying to figure out the secrets of AC power, and I've learned a little......
------Always A/B compare EVERY AC cable/conditioner/etc. against the same component directly in the wall. Very sobering, frustrating, and an often forgotten step when comparing many individual products with each other......DIRECTLY in the wall will win 80% of the time over the BEST connditioners for SLAM and authority, and all passive conditioners seem to destroy the bottom octaves, as they somewhat filter the top RF, and it's modulation away. The theory is that the inevitable raised impedence of a passive capacitor kills it's jump from the wall to your gear. RESULT a LOT of us out there run naked gear, and pray it doesn't cook in a brownout.

------Balanced power drops the noise floor BING! 5-6 dbs or more, but it's not the holy grail, and spendy done right. But it's addictive on source components, the toughest challange in comprimises. Power Amps seem easy to me now;;;;just spend 200-400+ to taste, and go right into the wall.

------Strand microphony is very real, and glaring in AC signal (speaker also) so I would steer clear of KIMBER or convential braid, and if you can afford it, chase flat conductor designs for achieving CLEAN. (Note= I love KIMBER in interconnects)
I love my PSAUDIOPowerplant, but can't understand why Paul has decided to sell prehistoric old ideas for AC cables(???) All donut filters compress the highs to my ear;;; an older Audioquest cable w/donut seems to clearly and easily demonstrate this;;; has he ever listened to the competition in AC cables?? Oh well, they have treated me well, I shouldn't bitch, and it's all system dependant, so who knows............

------THe floating shield, combined with a large gauge, creates a low pass filter, e.g. The modern Powercord is indeed revolutionary, and eventually all will hear it's clear benefit, if they ever try listening. I say= chase cords, not conditioning on a lower budget, if your gear can put up with no circuit protection. Conditioning is a can of worms with no clear solution;;; good luck!!!

------If you are not hearing any change with a Power cord in your system, try an AC Master Coupler (not an AC --coupler) by Sysnergistic Research. It's a classic, and not my first choice for refinement, but you WILL hear a difference;;;; great bang for the buck.

Audiopheliac (Audiogon registration pending)
TWL is on the right track. In the price range you're looking I'm not sure you'll get an improvement as much as a difference. Power line conditioners, especially inexpensive ones are as likely to get in the way as not. I don't know if it's a need but I'd suggest making a few power cords with the $150. You can make out like a bandit by throwing together a few cords from the audioasylum site.
Good luck!
I have actually owned/tried/demo's all the power conditioners I mentioned. Yes, even $150 can make a difference if you choose the right one.
Spend your money improving the electrical path not patching with band-aids. Power conditioners may only help when and where you can not pull a dedicated line with a high quality ac outlet to feed your equipment. Always improve the most basic of signal paths first. Tom