I power from 10A bec with 4700 +1000 +1000 uF low ESR capacitor direct solder on raspi board, lenght of 18AWG wires 20 mm. I check power sequence with 1000MHz band pass Textronix, I can measure processes less than 1 nanoSec. No power problem.
Pi cam port crashed in moment of starting capture – Red led on Picapture short pulse in moment start Raspivid.
If power from weak 500mA USB source all work good – but throttled bad.