If you hadn't already installed the cap kit, I would tell you to replace all the caps in the PS section, although it's possible something else caused it to go bad.
There are some small transistors in the high voltage section that Well Gardner Support lists as possible suspects. If their site doesn't have a troubleshooting guide for the U5000, call the 1-800 number and ask their tech support for some suspects. (John is very helpful.)
When a D9200 I was working on had the same problem, they had me check and change those transistors, but the final solution ended up being bad caps in the PS section.
If it becomes too much of a headache, you could always spring for the K7500 chassis replacement they have on their site for the U5000.