ibook power cord issues?

[Jack Countryman]

On the dual usb iBook, I'm lately finding that after being plugged in for a
while, it stops charging...the 'ring' around the base of the plug is no
longer lighted, even though its all still plugged in.  Do these shut off if
they get hot, or why would it stop indicating the power connection/charge?

I find that in some instances, if I swap the plug in cord for the plug that
goes on the power 'brick' that it again charges for a while.

What would cause this?   How do I fix it?