Why have capacitors improved so much over the years?

For high voltages, 300 and higher including 1000 or more, I feel safer using polypropylene to electrolytic because of shelf life issues the former do not have and you can get polypropylene good for 1300 Volts for about the same price you would have to pay for banks of electrolytic capacitors wired in series and parallel to get rated 1800 Volts. The former are larger, 3" diameter but you can get an aluminum box 17" by 17" that will have enough room for two power supplied with chokes on the negative sides. I use fast solid state diodes with center taps on power supply transformers rather then risk the problems with high maintenance mercury vapor diodes and the isolation transformers for their cathodes that have to be pre-heated and could short circuit.

From the early eighties until the early nineties the transparency of audiophile-quality gear improved enormously.  This is almost certainly the improvement in passive part quality (mainly capacitors, but also to a degree in resistors.)  My observation is that J. Peter Moncrieffe in his publications and promotion of WonderCaps made believers out of many who had heretofore scoffed at the notion that these passive devices had a "sound".  Electrical engineering courses, of course, had not even considered these subjects.  I know for a fact that the folks that developed the HK Citations found part swapping a critical part of their development, at a time when virtually no one else was doing it.

Lou, what a well articulated post! Some of your quotes are priceless!

Yes, Lou's post was very good & made for some interesting reading. I can't understand either why manufacturers go through all the trouble of designing a piece of gear & then at the most critical point insert cheap caps.

I can't understand either why manufacturers go through all the trouble of designing a piece of gear & then at the most critical point insert cheap caps.

For one thing, a large manufacturer might pay a dollar for a cap which you might pay ten.

Adding $100 in parts cost is $500 out the door and $1000 in the store.

Many of the improvements effected by the great unwashed may be seen as detrimental by the designer in terms of sonics, reliability, etc.

An engineer, be it an all out, no holds barred or LoFi PoS has a specification of what it to be achieved and a budget to hold. Better caps could result in a flimsy chassis, under-sized heat sinks, lower quality PCB, cheaper switches, etc. etc.

There are plenty of Best of Everything manufacturers and their prices reflect it.

How many Joe HiFi tweaks are verified in engineering terms? Joe may think it better, but most may not.