[daj]

With equipment, however, that was designed under idealistic assumptions about the AC power, external measures are almost certainly required. I suppose that in some such cases, the designer has determined that the power will be conditioned externally, but this still leaves open the problem of crosstalk over the power cords between such gear. For instance, the combination of a CD player without power filtering that is plugged into the same outlet as a tube preamp that has a cascode magnetic cartridge gain stage with megahertz bandwidth and an unregulated supply seems likely to suffer audibly from clock injection from the CD player, especially if one or both pieces of gear have suboptimal internal grounding.

Still, although a fancy power cord that mainly comprises conductors in a jacket may be somewhat helpful under these conditions, it is going to have a small effect compared to a power conditioner, especially one that isolates each of its outputs from one another. Of course, under these conditions, if a fancy power cord has a genuine noise filtering network built into it (not just the cable parasitics), then it would be a marked improvement over any gauge of plain conductors, whether cabled, braided, shielded, zig-zagged, or dipped in lanolin.

I think a big problem is that many (or most) manufacturers aren't even aware of these issues, afterall, look at all the power supply designs in gear everywhere where they slap a big-ass capacitor right after a diode bridge, can you say massive current spike and loads of noise?  Even funnier is when they do it in tube gear, hey, let's put a 3,000uF cap after the diode bridge, or gee, how about a 200uF cap right after the tube rectifier?  Nevermind that the tube rectifier datasheet explicitly says "max size for first cap is 20uf, unless the first filter element is a choke", but I digress.

As for filtering out noise, it can be done but it's a pain in the butt, and frankly not too many people do it right.  Ideally you want to minimize the noise being generated by the gear, prevention afterall is always better than the cure.  Unfortunately, see above, not many people do it right.

So I guess what I'm saying is this.  Given today's inconsistently made gear, power cords can make a difference, but not as much as proper filtering nor a nice fully isolated power conditioning for each piece of gear.

Yes, indeedy. There are lots of amateurs designing analog gear all around, these days, not just audio. In audio, though, sometimes it seems like any DIY guy who manages to build something that doesn't blow up thinks that gear should be on the market, slaps a fancy face plate on it, and fires up the hype machine. Most people won't know the difference. Heck, even the designer hasn't got a clue. The situation is a boon at least to the power conditioner designers. Big, studly blue cans? Heyyy, that looks soooo cool! Of course, it's partly because schools are mainly turning out digital guys, and practically no one with lab experience, electromechanical grounding, or control system theory. But even the experienced digital guys eventually have to learn that we're analog boys, living in an analog world, or they won't even be able to get a data bus to work. Anyway, buyer beware, but how?