Dream multimedia quote on their website 12v 1A or 2A psu for the dm500,
12V 2A for the dm600,and 12V 3A for the dm800.
Power consumption for the dm500 is less than 10W at 12V ,thats only around 800mw, half the rating of the 2A psu you have.
The only reason to change the psu if its of poor...