cap for geckos

Hi,

Alan's box shows 4 geckos, all without capacitors at terminals 1 and
2. Mariss white paper says to put a 470uF capacitor across these 2
terminals if the cables from the power supply is more than ____
inches. I put the capacitor across the terminals irrespective of the
cable length. Which is a better practice?

Also, is there anywhere on the web where one can learn the theory
behind such things. As it is, one does not know what is the effect of
not connecting the capacitos, or what if one uses capacitors less or
more than 470uF, or what happens if one uses capacitors across the
bridge rectifier (power supply) of value less or more than calculated
from the formula in Mariss white paper?

Meneer