Series identical power supplies
Galvanically isolated means there is no DC coupling between the input and output.

Here is the best step by step on how to remove the ground strap on all except the 1st supply. Then add a bus resistor to enable the supply.

https://www.rchelination.com/index.php/tech-tips/how-to-setting-up-the-hp-dps-1200fb-power-supply

Y caps are line to ground used for line noise EMI filters.

PE is the Protective Earth ground.