Ron,

In the past 20 or so years I've seen about 6 lots of tant caps the were
polarity mis-labeled. They get quite hot and pop. One even smoked a trace
on the PWB. (My fault for making it too thin).

You can test caps by putting them directly across a DC supply at 1/2 the
rated voltage. The supply should be able to supply at least 1 amp. If the
cap gets hot in a few seconds its "+" lead (what ever its marking) is
connected to the "-" lead of the power supply. Wear safety goggles as com
caps can fail spectacularly. Also be careful touching them as they can
raise a blister.

Good luck - Ray Klein

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