Why don't higher end amplifiers come with a separate power chassis?

Yes, The  AGD Audions come with quality power cords.

There are some amp manufacturers who do think aftermarket power cords make a difference in sound quality.

I do not doubt that for a moment. One thing is certain, confirmational bias is powerful. If someone is convince something will not make a difference, it certainly will not. This mindset can be extraordinarily rigid and unreceptive. Debate will be pointless.

Charles

@pwayland - The effectiveness of a tiny bit of resistance in the power supply to reduce or eliminate noise should not be underestimated.  DC sources with a tiny resistor in the way are going to perform much better in terms of noise rejection.

This is why it drives me a little nuts to see audiophiles trying to use car battery cables all the way to the transformers. The resistance and inductance between you and the rest of the world is a plus.

Frankly I don't see how marginally dripping the voltage with a tiny resistor is going to achieve anything.

Seems to me the amplifier is deserving of a separate power box and all the rational to not do it doesn’t make sense. The impact on sound could be huge if done properly.

@emergingsoul Keeping the power supply as close to the output section as possible is really important. You can have some pretty heavy current moving about and best not to have voltage drops due to any distance. Sometimes though an outboard supply has to happen; when this is the case if you do it properly you have to jump through some hoops to prevent the distance from interfering with the performance of the amplifier circuit.

Frankly I don't see how marginally dripping the voltage with a tiny resistor is going to achieve anything.

It depends on the circuit and how the resistance is applied.