Sounds like the other power supplies ran out before they broke the 1.5 to 3 amps required to fully light a glow plug (max 3A at 1.5v = 4.5 watts). That last one though... 1.5A at 12v = 18 watts.
They're just like (exposed) light bulb filaments. Double the voltage and (if the power supply can handle it) you double the power.
But yea, we've all been there. Just learn from it and you'll be ahead for next time. Not like you did something really crazy like forget to add oil after an oil change... (I had to drive that guy to work for two months