I called an old friend who works as a technician and his take on the capacitor problem is as follows:
The power supply is a switching power supply, which is smaller, lighter, and cheaper than a more conventional power supply, but is also considerably less durable. From the beginning, the output has ripple AC current that the motherboard capacitors have to deal with, and as the capacitors within the power supply degenerate, there is an increasing amount of ripple current that further stresses the 6.3V 1500mF capacitors on the motherboard as they clean up the dirty voltage from the power supply. Low quality capacitors are part of the problem, but the use of a switching power supply is the actual root cause. Even with good capacitors, the design is not a long-lasting one.
If this is indeed the case, do any high-end computers use the old type of very solid (and very heavy) power supplies? With all the extra copper involved, this would probably double the weight of the machine, but if longevity is the goal, it would be an interesting option for those who could afford it.
I suppose machines that don't have to be left on 24/7 ought to be unplugged when not in use. Going back to my 25-year-old Sony TV. How long would it have lasted if it had been on 24/7? Not 25 years for sure! It's also a pre-remote control model, so when the power button is switched off, there's no current going to the circuitry inside.
What else. A few hardware things just in case anyone might be interested.
My remaining Dell Dimension-C's motherboard capacitors are bulging upward. I hadn't noticed earlier, as there is no leaking or hint of linking and they look fine visualy down inside the computer. By reaching in and touching the tops however, I can feel that they are bulging upward. After talking with my friend about power supplies, I had a look inside the 80W(!) power supply of my dead Dell Dimension-C. All looks fine visually... and most of the caps have a "K" on the top instead of an "X". I read somewhere that the "K" capacitors are better? I also read though that the capacitors can look fine visually but still be bad, so - without an oscilloscope - it's hard to say what condition the output power from that power supply is in. It certainly is a low-capacity power supply though! (By comparison, the custom box I have has a 300W rating.)
I dragged an old Epson box out of storage and installed the new board I bought last week in it. The power light comes on, but there is no other sign of life. I'm tired of wasting time on that board, so I think I'll just write it off. One good thing though, is that the old motherboard of the Epson machine has ten of the "K" capacitors that seem to be in good condition, so maybe I'll try putting them onto the board of the custom computer that is working with bulging capacitors that are just beginning to leak sightly (with black in the middle of the "X" on their tops).
The old Epson has a floppy drive and cable that utilizes a missing prong on the male side and a blocked over hole on the female side. The old cable thus would not plug into the board, so I had to change the cable to a newer type with no blocked over holes. What technical shift in floppy drives does this represent, if any?
New boards seem to be more square, while the board in the custom box I have is narrower and longer. This creates a mechanical problem, as the corner of the board competes with the CD/DVD drive for space.
Lyle (Hiroshi) Saxon