How do I determine what filter capacitors to use (power supply line)?

[roogadget]

How do I determine what power supply capacitors to use?

I am working with a module that has already provided me with with correct capacitors. (attacked)
However, I would like to know the reason or rather formula behind their decisions.

All of the resources I have found don't go into enough detail. It almost seems like picking these caps just comes from trail and error.
I've ask one of my professors and he pretty much told me to keep switching them until I find a cap that filters best...

any ideas?

[David Hess]

Usually just a bulk electrolytic capacitor is combined with a ceramic or film capacitor which provides a lower ESR at higher frequencies.  Multiple capacitors of different values might be used where series inductance is more of a problem like with leaded parts.

[malagas_on_fire]

it all comes to what is acceptable for you're circuit powering, in terms of... ripple :

https://en.wikipedia.org/wiki/Ripple_(electrical)

[german77]

If you want to know exactly witch capacitors to use you need to test them as each brand and type filters different frequencies. This is done with expensive equipment. I think Dave have made some videos about this. Usually using multiple capacitors of an order of magnitude value will give the best results.

If you go from 10mF....100uF, 10uf, 1uF, 100nF, 10nF....1pF. you will filter almost anything. But of course in practice having 9+ capacitors to filter a power supply will not be very practical. And will introduce other problems like the initial current spike. So one usually start adding a capacitors one by one looking for the best results. 2 to 4 capacitors will filter the most noise. Adding more will reduce even more but not by a significant amount.