Adding capacitors to a Quark 125B

[JPP]

What a terrific tutorial; thanks! One question: I noticed that the capacitors you're using are 330uf 35v, and I think somewhere else I saw that you definitely need 35v. Don't know if you chose those because you happened to have them or if you bought them specially for this purpose. If I'm buying them specially for this purpose, what are the ideal specs? (My poor knowledge of how electricity works, and for that matter, what a capacitor even is, is hurting me here...) Do you have a recommended source?