According to mm :
BTW, my new Motorola "Go Phone" phone came with a wall wart that has
two rings on the plug, plus the center hole. I was going to measure
the voltage soon, but since w'ere on the topic, can anyone tell me
anything about it. The label just says the output is 5.0V with the DC
symbol.

Why do they need two rings, and is the car charger whose plug fits the
jack, that I bought for 50cents at the Carroll County Hamfest, likely
to work or to ruin the phone?

The center pin or one of the rings may not be used at all, or, the
two rings may be connected together. Does the wallwart have a schematic
picture of the connector? They often do.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.