Why do designers/manufacturers...?

Jea48 is correct, power cords are not just power delivery. The measurable differences don't seem to be profound, but they can affect power amplifiers in particular in a number of ways.

First is the voltage drop across the cable. When I saw 40 watts lost in one of our power amps, the voltage drop across the cable was about 2.4 volts. But a cable has to have high frequency capability as well- anyone that knows power supplies knows why- the rectifiers in the power supply only turn on (commutate being the technical term) when the voltage from the power transformer is higher than that of the filter caps.

Now the amp only drains the filter caps a small amount between AC power cycles. So the result is that the rectifiers only commutate on peaks of the AC waveform, perhaps only for a very brief time! So if the cord lacks high frequency capability, the power supply won't charge up properly and you can hear the result, plus you can measure the power supply voltage as well.

ROMEX works surprisingly well, so the real problem is in the power cord, not the wall wiring unless the building is quite old. However it is illegal to use solid core wire in an AC power cord. Thus, the cable has to flex, can't have any voltage drops (the problem areas are often at the terminations, but the cord itself can heat up from voltage drops as well) and has to have good bandwidth.

If the cord satisfies these requirements it will work fine and won't matter what brand it is.

Perhaps it is as simple as Dealers want large margins so that they can discount because we, the customer, want a discount. We always feel better when we get a discount... :)

So, manufacturers not tweaking, or using the supposed best parts, is perhaps our fault!... maybe :)

We use an IEC connector for the simple reason that no matter what cord we put on the amp, the likelihood is high that it will be discarded anyway in favor of the audiophile's preference.

We do however make sure we have the best resistors and capacitors in the actual circuit, or at least have them optionally available. I have seen too many times where someone thought they could improve the amp or preamp, only to turn it into a rat's nest in the process. Believe it or not, neat wiring often sounds better since stray capacitance is better controlled!

Atma-sphere,

Maybe you could correct my understanding, but I thought most power in the US is at 60Hz? Which high frequencies are you referring on a potential power cord?

What most people don't understand is that the first thing an the power from the wall does when it hits your amp is go through a transformer to cut down the voltage and then hit the rectifier which is converts it to DC. Yes the cap converts that rectified signal to a smooth DC line. I have used some very fast scopes and never seen the DC on that line changing. Most listening at home is well under 30watts so the power through the cord is relatively low. Even if there is fluctuation in that DC voltage, on a SS design is dropped again by a regulator to the rail which gives the whole system margin for any voltage regulation.

The only way one should here an issue caused by the power supply (including the cord) is if the DC voltage fluctuated and unless you have the volume turned up to 11, it doesn't.

I have been to some very big name audio manufacturers and as far as tweaks at audio shows, they use them because the parts are given to them to use, but at the home office, they use cheapo cables and power cords. Either these large companies are just cheap, deaf, or don't believe in tweaks, I don't know, but I am guessing it's the last one. Engineers love numbers and most tweaks can't be proven by numbers.
For cables that rob a system of 40% of their power, that means there the equivalent of a 40 ohm resistor on the cable. Whoever made that cable should be fined and put out of business.