You can, but if you start pulling more than 45W you will melt the power supply. My general rule of thumb is to not exceed 80% of electrical ratings for more than a few minutes or things get really hot and degrade fast. That leaves you with 36W to use safely, which is still 3A @ 12V.
That charger is rated at 200W. Ideally you want a power supply that at least matches that to use it to it's full potential.