how to select capacitor values
In order to how much cap to use where, you need to know a fair bit about capacitors in general:


The different types (electrolytic, film, ceramic, tantalum, OS-CON, metalized film, etc.)
Their characteristics (impedance, ESR, ESL, polarity, temperature rise, dielectric, etc.)
Their failure modes (aging, over voltage, reverse voltage, thermal runaway, etc.)


You also really need to know why a cap is being used for a particular purpose, such as:


Power supply output caps: less to do with holding the voltage up, more to do with ensuring the ripple voltage isn't excessive
Power supply input bulk capacitors: mainly to do with hold-up time (keeping the output up for a short time after the input is removed)
EMI filter: providing specific frequency attenuation, in coordination with other filter components
Decoupling: providing instantaneous current to a circuit; a function of the circuit and the physical layout


Good luck with your knowledge quest. It will take some time but as you gain experience, things will get clearer.