In my case the problem is space, and also temperature. It is a switched power supply, the components take up a lot of internal space and due to the power being 750W it heats up well, has forced ventilation, but I believe that using a battery there is not very recommendable. I'm thinking of using a W25Q64 instead of the SD card, and don't use backup power supply, probably data loss must occur at some point. I want to collect data for a possible intermittent issue. The user claims power supply failure during use, but when testing on the bench, no defect occurs. As the operation of the power supply depends on external control, I believe that data collection can help to find this possible failure that may be occurring, whether internally or externally. The equipment that uses the power supply does not accompany the power supply when it is sent for maintenance, so it is difficult to evaluate.
About the choice of capacitor, yes, it really is a bit complex, here is a post from a manufacturer: