old power supply  (per rail)  (just the unregulated primary)   680uf x 2 caps in series, about 600v.  total energy storage  61 joules   new power supply 500v 1 x 680uf cap  total energy storage 85 joules   so you can certainly get away with 470uf which is 58 joules and that one is only 60mm high   but if you are insane, you can go with the 1000uf cap which is still 40mm diameter but 105mm high  and get 125 joules   I'm clearly a fan of overkill, but 125 joules is in the range of a he