i think i found the info that i was looking for
NOTE: 240VDC function will not work when 775595-B21is installed in 745813-B21. Only AC input will be enable.
NOTE: Redundant AC Power Input Modules do not share power. Redundant AC Power Input Module #1 is the primary AC Power Input Module. Redundant AC Power Input Module #2 is the backup AC Power Input Module.
HPE Entry-Level Power Supplies - document.
It will be OK just to put 775595-B21 but they will act as active and passive PSUs ..