There is no standard method to transfer the variance (PPV) between projects.
As a workaround you might consider update the standard cost so it will reflect the real PO price (including the current variance). You might need to update the item cost just before entering the project transfer transaction in Inventory.
Another method could be to enter two miscellaneous expenditure in Projects Costing, one will reduce the PPV amount from project A, and the second will charge the same amount to project B.
You can use a Expenditure Type to capture PPV separate from the STD cost in the PJM parameters.
Once it flows into Projects using Allocation Rule send these expenditures to another Project.
Hope this helps.
The Allocation method is fine when you have all project transfers of project A to project B. Then you might allocate all PPV summarized in project A to project B.
In case you want to deal with individual item/PPV transaction the project allocation will not help you, and the solution need to deal with individual transaction amount.
I understand you want to allocate all cost incurred on project A to project B. If you setup the allocation rule to do that, each run of the allocation process will generate one expenditure item on the target project.
Therefore, you can have only one expenditure type for such expenditure item.
If you want to keep the list of expenditure types of project A so cost will be transfered to identical expenditure types in project B, you might consider setting up multiple allocation rules.
You need to setup allocations source by resource list, where the resource list is defined by expenditure types. The summarization process will summarize the total amount of each expenditure type on project A. You will need to setup each allocation rule for an individual expenditure type (resource) in project A. Foe each such allocation rule you set the target expenditure type to equal the source expenditure type. Be sure to have all you expenditure types with an additional expenditure type class of miscellaneous.