I started out with the Digikey web site, specifying the diameter, lead spacing, capacity through to "capacity + a couple of values", minimum voltage through to something sane and then just sorting on ripple current. Then I could use the ESR to figure out which looked "best" for the application.
I found the RS web site easier to use to do that sort of sorting, then I picked a couple of readily available cap series (like Panasonic FS & FR for example) and just worked my way through the data sheet. Comparing a couple of data sheets made it a bit easier to narrow down some "likely suspects" to then check availability on.
Even better when the data sheet lists dimensions vs ripple current for various voltages. Can just start the selection process on physical sizes / lead spacings.
An interesting process and looks like it got me a lot closer to viable replacements for the Sprague 672Ds that came out. Can't find legit data sheets for the 90's versions in the scope, but when comparing to the modern versions by dimension it looks like I got the ESR and ripple current "close enough" while bumping the capacitance up a size or two and greatly exceeding the original voltage rating :
https://www.vishay.com/docs/42054/672d.pdfI'm sure it'll go, and given the amount of use it sees, the caps will probably be the last thing to cark it. In fact it probably would have been ok with the original set of caps I ordered, which were based on capacity & voltage, and were ~33% of the original sizes and ripple current specs. I'll put them into "service stock". The reality is the thing has a crack over 1000h on the clock, if I wasn't worried about cap leakage I'd have left them all in place. They all measured out in capacity and ESR as perfectly fine.
Your logic is sound ... Once you have capacity, ripple current rating is the key factor and if you end up with a higher voltage rating - who cares?
Well, the reason I originally asked was uncertainty around long term severe electrolytic de-rating and whether there was anything to be concerned about. A bit like unused caps needing reforming, would running an electro at less than 10% of its rated voltage have any detrimental effects? My gut and experience says no, but there are much more experienced heads here so I thought I'd avail myself of that wisdom. I know enough to know what I don't know.