What to do with 90v/8v transformer? Leakage tester?

[Steve Blackdog]

" How do work out that capacitors should be 2200 or 4700 uf"

Technically, it is not simple.
Realistically, there is a small available range of capacitance values.
Too small of a value can result in excess ripple under severe load.
Too high of a value can cause an unnecessary inrush current.

The true capacitance value depends on voltage, current draw, resistance of the transformer and the diodes........

Here is a good read:
http://www.skillbank.co.uk/psu/smoothing.htm

perfecto! Thanks