I'm using an old PC power supply rated at 25A. The strange thing is that when one shift register is lighting up a single row, its plenty bright enough. But when I start to light other rows, they all get dimmer. To clarify its like one row i am at 100% brightness. Two rows, everything is at 75% brightness. Three rows 50%..and so on. This is kind of boggling me because the shift register circuits are relatively independent of each other except for the power source. The PSU has a 10ohm 10 watt resistor as a load to turn it on. I connect the shift registers in parellel with this load.