Determine how much resistance is on the whole circuit. Calculating parallel resistance involves adding the reciprocals of the resistors' values. A 3-ohm, 4-oh and 5-ohm resistor on a parallel circuit produce 0.75 ohm of resistance.
Replace the original power supply with a higher-rated power supply. More voltage means proportionately more current. For example, a 15-volt power supply connected to 3 ohms of resistance yields 5 amperes. Those same resistors would allow a current of 6.34 amperes when connected to a 20-volt power supply. However, be sure you don't overload the components. Check their ratings beforehand.
Add another power supply in parallel for another method. This is done by connecting positive terminal to positive terminal and negative to negative. Use alligator clips or electrical tape to secure the wires.
Remove some resistors from the circuit, if possible. Fewer resistors, when connected to the same voltage, allow a larger current to pass through.