"Shaun Eli" wrote in message
Anyway, I stopped believing in trusting advice given in mom & pop
hardware stores. The first time the clerk told me, when I was buying
lamp cord, which color was for positive and which for negative... it
took me ten minutes to explain alternating current to him.

Uh, take a good look at some of your cords; note the subtle difference.
Take a look at the plugs for polarity. If you don't see the differences,
go to a good hardware store and ask the guy about it.