They do make a difference - or at least they can - but, only sometimes or not. But, as near as I understand it, one of the biggest stumbling blocks for PC designers is proper geometry vs gauge vs length. The big goal being to lower impedance. Noise pickup, or cancellation (or even passive reduction), is another factor. One problem with it all is that this balance of those 3 factors is pretty much dependent upon the given application: whether you intend to use the PC to supply a source (and whether that is digital or analog), or a pre or an amp (even tube or SS??), and so on. But, even with different cords for different apps, there is still another problem: the in-wall wiring in your home. Not only the wiring itself, but what kind of load is being applied through it to each circuit branch in your breaker box. To keep voltages stable over time (theoretically speaking anyway) your home circuit branches from the box should each be given a fairly steady load, or draw, that is only somewhat below the rating on each breaker (safely close to maximum). So, if you have, say, a 15-amp circuit, with a good, relatively stable draw of around, say, 10 or 12 amps most of the time, then this results in voltage stability for that circuit. But, OTOH, if you have, say, a 30-amp circuit that nothing is ever plugged into, then this can contribute to voltage instability in the rest of your house. To us audiophiles, that translates into those day-to-day, time-of-day changes in sound that can plague our systems, sometimes somewhat predictably, although sometimes not. It is often assumed that these voltage swings are always coming from the power outside the home (which can happen), but in actuality it may more often originate from inside the home. Voltage regulators would appear to be a solution, but, ironically, they are usually just as susceptible to these fluctuations as our systems are(!). But, into this unpredictable environment the PC designer must go, but the question is how. I know all the complexities are rather hard to fathom, but that's really my point. Even for the PC designer, there is no way to arrive at any perfect solution under all circumstances. Not only is every system different, but every home's electrical system is different as well. No PC will independently solve an in-home voltage instability (just good old properly designed and utilized circuits can account for a lot of that). But, at least one thing to take away here is that there can be at least some PC solutions that are perhaps very good, or even excellent, in many, or even most, situations much of the time. However, in this context, that means that those PC's are likely not first 'dreamed up' on paper by the engineer, but instead arrived at by trial and error and are necessarily 'developed' over an extended period of time...and only, it would seem, by repeatedly testing under real-world conditions - not in a lab. Which makers will be doing just that and whether or not the cords would make the kinds of changes we may be hoping for in our systems and in our own homes is still the (you-fill-in-the-amount)-dollar question. For my own money, Alan Maher Designs has been doing this for a few years now and is a company I've had excellent results with, but their PC's also utilize passive noise reduction, which, although a 'whole 'nuther thing' in itself if you will, it has worked out to be a big advantage over other makers, for me. Hope all this helps.
