I have a GE gas cooktop that runs on propane. It doesn't seem very powerful, I have used much cheaper stoves that run on propane that boil water much faster. Is there any way I can increase its output ?

Where I would start is by checking your gas pressure. You will need a pressure gauge to achieve this. Perhaps your gas pressure isn't high enough. However DO NOT adjust the pressure without using a gauge, and NEVER adjust the pressre higher than what the data plate calls for.

You may also want to check the orfice to make sure its not clogged on the burner.