For series power supply connections, add reverse-diodes so the weaker PSU does not get damaged.
It's like two power supplies arm wrestling if the load is near maximum.
Yes agreed, this could be the case with two series'd power supplies which both dont have soft start, and there is a big external cap across the "total" (doubled) output....the weaker power supply could possibly get reverse polarity'd during the startup surge....and so the diode is needed.....even then there'd still be a diode drop of reverse polarity on the weaker one , which i doubt would do its electrolytics any good. (assuming it had electrolytics).
This is why its good to have the soft start.
You can buy (or make) “boxes” which have transistors in them which act in the linear mode, and there is error amplifier circuitry in there which makes them all pass the same current….so you connect the various power supplies to this box and it equalises the current output from all of them…….and gives you your one single high current output.
There are more elegant ways to do it, but if you just have a couple of supplies that you want to put together , then this is a crude solution which will do the job for you.