Hi, yes an electrolytic capacitor, at least 1000uF 16v in value, even 2200uF 16v would be better. Voltage rating can be higher but i wouldnt go any lower than 16 volts. Will the power supply be using a voltage regulator at all, or unregulated? Regulated is much better (less noise/hum).
I have built power supplies for guitar pedalboards in the past using LM317T adjustable voltage regulators, set for 9 volts. This gives you up to 1.5 amps capacity to run effects, depending on the transformer amperage you are using. It all depends on what effects pedals are being used.. delay effects, ie digital delays, chorus/flangers etc are more power hungry than, say overdrive or wah pedals.
hope this helps! being a muso myself, im happy to help out some more if needed
Cheers... Mitch
