Just to clear up some confusion: Assume that your load (breadboard or whatever) is rated at 12V, 500mA. You could run this load with a power-supply rated at 12V 100A, or a car battery (which is about 12.6V) but capable of delivering 1200A (Cold Cranking Current rating) and your load would still only DRAW a maximum of 500mA!!!!
Think of it this way: 12V is the CAUSE, 500mA is the EFFECT. The load knows nothing about how much current the supply can DELIVER, it only draws what it needs off the supply. The supplies' job is to keep the voltage constant at 12V, and for that to happen, it needs to deliver a minimum of 500mA.
Nobody cares if the supply is capable of delivering more than 500mA, unless you accidentally create a short circuit or miswire your circuit. That is why supplies used for lab work usually have built-in current limiting, so that you can set the current limiter a bit higher than your circuit under test will draw, thereby limiting the amount of smoke in case you screw up!