Create New Table from two tables mixing columns and rows

You really want to do this in Power Query, not in DAX.

1. Click Transform in the Power BI ribbon.
2. Find the Requirements table, click on the PO column, and click MERGE on the Home ribbon of Power Query.
3. Select the Delivery table and also click on the PO column.
4. Select Left Outer Join. This is pretty safe as it seems you will have requirements but not delivery on occasion, but never delivery without requirement. This will pull everything from the Requirements table and all Delivery items that match, and will return NULL when they don't
5. Click on the double-arrow in the upper right of the new column that has 'Table' listed all through it and check the Date_Deliv and Qty_Deliv columns. Be sure you uncheck the "keep column name" box at the bottom. Click ok.
6. That is your new table.

Now you need to go to the Delivery table and right-click and uncheck "Enable Load" so it doesn't load into the model. Your Requirements table will now load with all of the relevant columns.

Microsoft has a visual walkthough here.

Hi JoaoMS 

Kindly check below results:

let
    Source = Table.NestedJoin(Requirement_Table, {"PO"}, Delivery_Table, {"PO"}, "Delivery_Table", JoinKind.LeftOuter),
    #"Expanded Delivery_Table" = Table.ExpandTableColumn(Source, "Delivery_Table", {"PO", "Date_Deliv", "Qty_Deliv"}, {"Delivery_Table.PO", "Delivery_Table.Date_Deliv", "Delivery_Table.Qty_Deliv"}),
    #"Removed Columns" = Table.RemoveColumns(#"Expanded Delivery_Table",{"Delivery_Table.PO"})
in
    #"Removed Columns"

Pbix attached.

Thank you, it works perfect!