Difference Between PRC: Transaction Import & PRC: Interface Supplier Costs

Dear All Experts,

Can you please let me know what is the difference between PRC: Transaction Import & PRC: Interface Supplier Cost?

As I am facing here one issue that we have two nature of items i.e:

Inventory & Expense.

When PO is created of Expense items along with all Project related information into distribution is entered, its is coming into projects via PRC: Interface Supplier Costs process.

But when PO is created with inventory item the distribution field is freeze for projects information in PO so we need to make its destination as expense then application allows you to enter the project related information in PO distribution. So after entering all information when I run PRC: Interface Supplier Costs there is no record shows. Why this issue comes.