These 18,000uf 20v caps (big orange cap in picture below) are hard to find and if you do it will cost you lots. Read on for a simple solution for this problem.
All you need to do is get yourself 2 10,000uf (16v or higher) caps and connected them in parallel. Electrically this will add to 20,000uf which is more then enough for these old PS. In parallel I mean hooking the "-" side to the "-" side and do the same to the "+" side (+ to +) and then connect them to PS board just as you would any other cap.