Assuming thay a new bulb will also be just as dim.... then the problem is likely in the wiring.
Since it is just the one light, the best guess would be a bad splice or connection.
Low voltage lights are powered by transformers with very limited power output. Other causes of dim light(s) I have found have included:
-too much voltage drop, caused by too long of a wire;
-too many lights n the transformer; and,
-different circuits (some power supplies have more than one output circuit) interconnected.
