So I've been building a 20x20 word clock with 400 neopixel led's. Power has by far been the most challenging part of the build. Currently I have a PC power supply with 2 12v 14A pins, and 2 5v 24A pins. I have split the strip into halfs with the two 5v pins connected to each half respectively. I also have one of the 12v pins connected to the arduino with the VIN pin. I've programmed it to cycle through using the rainbow script but there is quite a strong flickering. I have no idea what's causing it or how to stop it. Please help!