Hi Prateek,
Little batteries or wall-wart AC-DC adapters cannot give "any" amount of current because they have an internal resistance that limits the max current. The more current that is drawn then the lower becomes the voltage. A new little 9V alkaline battery can give about 500mA to a short for a few seconds. So its internal resistance when new is 9V/500mA= 18 ohms which keeps increasing (and the max current keeps decreasing) as the battery runs down.
A voltage source should have a current rating where its output voltage drops no more than a certain percentage with its rated current, and a rated max amount of current where damage to it won't occur.