electrical help wanted

Designing a PS for Gecko drivers.
The transformer gives out 50-0-50 what size capacitor should I use ?
ie 50v rating or 100v and the bigger the capacitance the better or what?
I remember in the OLD days that one put a capacitor across the output
then a resistor inline and another capacitor across the output. I
suspect this was great for the ripple effect but perhaps the Gecko
dont care.
Brian Fairey.