Power supply DC Tap switch prototyping 1

I'm going through some of the tradeoffs right now with the power supply, transformers are heavy but easy to switch, SMPS are light and powerful, but we need DC switchgear for them that doesn't get stuck latched up.
I found the single mosfet is fine, but I'm going to need more reliability, like maybe 30 years worth, so we're going to go with 2 mos in parallel, hopefully one doesn't current hog.
We also found the SMPS was drooping about 20%, which is unfortunate. I expect that much droop from a transformer, but not a smps. So we are going to try some 5V units with higher current rating so we are more inside their performance envelope, I expect 4.6V at 40A, so we'll see how close I am to that estimate.
As a consequence of the DC switchgear, each tap changer will require its own isolated power source, which is a setback, but we are hoping for long life arc free switching, so that is something that has to be dealt with.