Any electricians on fluther?

Im trying to make an LED array for one of my fish tanks and had some questions about the power supply. I took an old laptop power supply and cut off the plug right before where it plugs into the “brick” well there were three wires so i didnt know how to figure out which was pos and neg but i got that all figured out now (funny story involving PnL, fire, and explosions) anyway my question now is, did that brick act as some sort of resistor? is there anyway to know,short of getting something to measure the voltage coming out of this(im poor right now). According to the “brick” its 12v but like i said, dont know if that limited the electricity coming out of the wall or not. Thanks