Hi,
This depends on what you like to filter.
12v and 5v output lines of a 300W PC power supply. This reminds me of an OT question: A 4700uF electrolyte capacitor is placed where the 4-pin PC power supply connector enters my board. Once upon the time, I was experiencing a problem with this arrangement: Right after switching on the system, the PCPS was automatically turned off. A former friend of mine said that it's because of the huge current rush to the 4700uF capacitor that makes the power supply "think" it's shorted. Then he adivsed me to parallel a resistor with the 4700uF capacitor to increase it's RC and hence the time needed to fill the capacitor. It worked, But now I can't figure out how to calculate/estimate this resistor.
Best.