Hi Ankita,
Not sure what is the reason for the different PO types and numbers but if you are looking at creating different PO types and their associated number in one backend system, you can use BADI BBP_ECS_PO_OUT_BADI to put in the logic. This is so that the system knows when to use which PO type, etc. This BADI is for an extended classic scenario.
Regards
SF