I live in NY and have found power conditioning and aftermarket power cords to be highly beneficial in my system. I used to use the Power Wedge 116 in my main rig (now used for my headphone set up with an Ultimate Outlet) and it was good for what it was 10 years ago. I think the isolation transformers were probably a limiting factor. I came to find large parallel filtering provided greater benefit than the use of isolation transformers, which are current limited (and will burn out with too great a continued draw.)
I used to use ESP Essence Power Cords throughout my system - I had tried Synergistic Research Reference which had great rhythm but too small a soundstage, 1st generation Electraglides which increased dynamics to an incredible level but had almost too lush a midrange - the ESPs were the best balanced in terms of overall performance, and I opted for "neutrality". These days, I've been won over by the sound my system produces using the PS Audio line of gear. I've heard improvements using the unlikeliest of tweaks, the Power Port. Using this duplex outlet on my dedicated line, the noise floor drops & grain is reduced - it's quite surprising. I use the Power Director 4.7 in conjunction with parallel filters plugged into adjacent outlets. I almost opted for a P500 Power Plant, but it didn't offer enough outlets for my entire system. A PS Audio xStream Statement feeds the Power Director and each component of my system (with the exception of the turntable.) I normally try to avoid cables with PVC sheathing (I find they produce smeared sound relative to the treble & timing with interconnects and AES/EBU) but have to say the Statements with the ferrite impregnated PVC help quite a bit. The PVC is kept relatively far from the conductors and is not the dielectric that comes directly in contact with metal. A friend of mine uses the Shunyata Hydra system, and he consistently gets great sound. I might try some of his Shunyata cords at some point, but I'm very pleased with the xStream Statement cables - they may very well be the best power cords I've tried in the last 10 years. I know markl cared for the PS Audio power cord he tried in his shootout the least of all - I haven't tried the one he used, so can't offer any thoughts.
While incremental improvements can be heard as you do things bit by bit, a sound system needs to be treated as a system, as a whole; I've come to feel power conditioning and power cords have to come hand in hand. That said, I understand overhauling everything at once may not be a realistic or practical consideration. I agree with most of what markl had to say, but if upgrading in stages, I would recommend conditioning first, so that the entire system benefits. Then treat source, amp and preamp. Depending on the power supplies in your gear, you might find more dramatic differences popping a cord on the amp first. If you condition your entire system first, it might make it easier to hear the improvements the cords make afterwards.
Best bang for the buck might be a PS Audio Ultimate Outlet, which uses a balun to cancel noise on your line. The improvement is clearly audible. You can probably get one used in the $200-250 range.
There used to be a product that you could plug into your AC line that amplified the noise so you could hear it. I think it was called the Sniffer. A friend of mine picked one up to play with, but I don't know how practical it really is once you know you've got noisy lines. Better to clean your juice and just use your ears and listen. Some people insist on not trying things firsthand because of what they think they know, forgetting they might not know enough. Let your ears be the judge.
*Edit*
The Noise Sniffer:
http://www.audioprism.com/noisesniffer.html
