I want to build a power supply from scratch for the fun of it. And because I need one. For some weeks I have searched for one I dream about (2USB out, 0-30V 5A+, 5V, 12V) the price for those is out of question. So making one is kind of the only solution.
Today my workplace wanted to dump an old Oltronix B32-20R with a really nice blue anodized cabinet because it blows fuses 
The fault was easy to fix. So now I wonder what to do with it.
Specs:
600W / 0-32V / 20A / ext line sense / line regulation 1mV / 100% load regulation 7mV / 0.5 RMS mV /22kg (48lbs).
It’s an old beast of a power supply
(Produced 78-95)
So now you have a FREE, working supply that does the 0-30V. And a nice one at that.
Nothing there stopping you from building another supply, since having more than one is always good.
Do I sell it to finance a nice ring transformer? Or gut it and use the cabinet for the project 
Neither. Just keep it as it is. Unexciting, but practical.
What price can be expected if I try to sell it?
Not a lot. Not enough to buy a whole power supply's worth of new parts. And selling a nice working power supply to buy parts to make another power supply is... not likely to bring satisfaction.
How long can you expect the caps to be functional?
Depends on their usage history and original quality. Some last forever.
What about the expectation on transformer life? Don't want to ship it and get a angry phone because it died after a short time.
Simplify! Just don't sell it.
For a +5V and +12V supply, you realize virtually any piece of discarded office electronics will provide that? Old photocopiers, printers, LCD displays, etc, often have a such a supply as a separate module, sometimes switchmode, sometimes linear, that can be built into a simple box by itself. And the front panels of discarded PCs will often give a nice detachable panel with a couple of USB ports that can be built into your power supply box (with suitable current limiting) for your USB power out.
After you have some working, reliable power supplies, then it's a lot easier to start a project to design one from scratch.