Large external capacitor will reduce output ripple. However, it will also increase input current surges during startup. To calculate peak input current, please refer to "SIMO Soft-Start" section on pg 65 of the MAX77650/MAX77651 datasheet (Rev 6 7/18).
There is built-in LDO in the MAX77650 that can be powered by one of the SIMO outputs to provide a low noise output power supply for noise-sensitive circuits.