How to figure out the maximum throughput on a capacitor?
If you can tolerate X% spike or dip from charging a load cap, then the cap on the source must be 1/X times bigger.  Like 10x bigger.  Bad idea.

So if load cap is 0.01F (huge) and assuming this cap has a very very  low series resistance {ESR spec} the rate of voltage charging will be limited by your supply current.  

> Formula=>  Time to reach ~ 63% difference voltage change  =T = Volts/Amps * Farads [sec] = "time constant"

Thus T = 20V/10A *0.01F = 0.02 seconds
However if load is already using 8A leaving 2A spare , it will take 5x longer  = 100ms and if 63~ % is nit high enough , you need to wait another couple time constants, to get to 95% or  3T= 300ms in this hypothetical scenario.

To reduce this down x10 in time you need a current 10x  bigger or 100A, which would over heat the cap. (Fizz boom)

S0 the cap needs to tolerate 200Watts for 20ms.

Not good idea, To increase current and reduce dip duration.

Better idea is use an inrush current limiter (metal oxide ICL .. cheap ) rated for X Amps and wait as long as it takes to safely charge up this supercap.

Need specs on part to check.

May I ask why you need to make a rapid charge?