In that case it sound like you have a blown fuse. I'd check that first.
(You are of course aware that the socket only gets power after the engine has started)
That said, the armrest power socket isn't very practical for powering something to be used on the dash. I fitted an expansion socket i the passenger foot well, which draws power from the wires going into the socket in the armrest. Its easy to root the wire under the center console.