On Thu, 19 Nov 2009 21:44:36 -0800, Daniel Prince
wrote:

I have read that electrolytic capacitors are the least reliable
component in power supplies.

Not exactly. The problem seems to be a mixture of counterfeit
electrolyte in some low-ESR electrolytics, manufacturers using
electrolytics that are operating far too close to their rated working
voltage, and too high a working temperature.

Lifetime on electrolytics is predictable and calculatable:
http://www.edn.com/article/CA6588368.html
http://www.illinoiscapacitor.com/techcenter/lifecalculators.asp
http://powerelectronics.com/mag/power_optimize_electrolytic_capacitor/
If you plug the operating temperature, working voltage, etc of your
favorite motherboard or power supply into the formula, you'll find
fairly short predicted lifetimes. Note that the operating temperature
is NOT the ambient or case temp. When you shove a bunch of ripple
current through a capacitor, it will get hot from the internal
resistance. Measure the temperature with an IR optical thermometer
for a better value.

The counterfeit electrolyte problem is probably what you're seeing on
motherboards. The crud is still in the system even 10 years after the
initial introduction. Some history:
http://en.wikipedia.org/wiki/Bad_capacitors
http://www.badcaps.net/pages.php?vid=4

I have also read that there are
motherboards with solid polymer capacitors.

Sure. However, they're very difficult to identify without back
tracking the part number or chopping one in half and looking for the
black goo inside. The clue is that they tend to be short and not very
tall, while conventional electrolytics are much taller:
http://www.niccomp.com/NIC1202_InFocus.pdf
http://www.mec-italy.it/pdf/nic/nspzr.pdf

The caps in the photo really are solid polymer caps.
http://www.capacitorsplus.com/whatis.htm

Are there any power
supplies with solid polymer capacitors?

Dunno and too lazy to tear apart a PS and check.

Thank you in advance for
all replies.

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