how to choose right power type for HPE DL server series

[Sovann007]

How to choose right power core HPE DL serious for example DL380, 360 ...
Mostly I sellect NEW HPE ProLiant Servers offer Flex Slot Power Supplie

HPE 500W Flex Slot Platinum Hot Plug Power Supply Kit x 2

and it show warning message 
" NEW HPE ProLiant Servers offer Flex Slot Power Supplies that come in multiple power ratings to allow you to pick the Right Size to fit your configuration. This provides you with the advantage of reducing and reclaiming lost power. By selecting the right sized power supply you will be providing facilities with a nameplate rating that is much closer to actual power your server uses. In order to select the right size power supply for your ProLiant Server it is 'highly recommended' that you use the 'HPE Power Advisor' located at ' https://paonline56.itcs.hpe.com/?Page=Index' to determine the right size power supply for your server needs.

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