MAX7221 not always powering on
The MAX7221 / MAX7219 datasheet specifies that 


  To minimize power-supply ripple due to the peak digit driver currents, connect a 10µF electrolytic and a 0.1µF ceramic capacitor between V+ and GND as close to the device as possible.


But the demo breadboard circuit that Kevin Darrah assembles in This YouTube video uses a higher value 100µF electrolytic.

I've always thought this is a power problem (a hunch rather than any real engineering know-how).

I tried Kevin's capacitor and it worked.