How do voltage, resistance and amperage work? (In DC circuits)
Yes, 12 V on a 150 &Omega; resistor causes 80 mA to flow.  That is because volts are volts, regardless of how they are being produced.

The difference between the 8 AAs and a car battery is that the car battery can provide more current if the load tries to draw it.  A 150 &Omega; resistor will always try to draw 80 mA when 12 V is applied to it.  Both the AAs and the car battery can do that, so no problem.

However, suppose you had a 1 &Omega; resistor instead.  That will draw 12 A if you apply 12 V across it.  The car battery can easily do that, so that's exactly what will happen.  The AAs can't do that, so something has to give.  What gives is that the AA batteries won't put out 1.5 V per cell anymore.  The voltage will go down so that the current the resistor draws will go down, to a level the batteries can sustain.  In this case, the AAs would be getting used up rapidly, so the voltage will keep going down and down as the batteries become more and more depleated.

A similar thing will happen with power supplies.  If you have a 12 V 12 A power supply, it can maintain the 12 V across the 1 &Omega; resistor indefinitely.  If you only have a 12 V 5 A supply, then it won't be able to maintain 12 V.  It will blow a fuse, shut down, go into current limit mode, or something else.  What it won't do is keep the output at 12 V.  If it could, it would be marked as a 12 A supply and sell for more money.

In the case of current limiting, you can use Ohm's law again to figure out what the voltage across the resistor will be.  Let's say the supply has a accurate current limit set to 5 A.  That means it puts out 12 V or 5 A, which ever results in less.  Since the 1 &Omega; resistor would require 12 A and the supply can't do that, it will regulate its output to 5 A instead.  (5 A)(1 &Omega;) = 5 V, which is what the supply will put out with the resistor connected.