V = I × R Volts are set, Resistance is set (you) Leaving I variable. The voltage that is set, and the resistance that is set, will determine how much amps is tried to be pulled. However Power sources have max amps they can provide. Their A ratings are not the amps that are forced at all times, but their max that can be delivered. If the power source doesn't provide enough max amps (* voltage, aka Watts) for your level of R, then you don't get smoked / light up.