Hi CCbooks,
That's a great question. As I'm sure you know, QuickBooks Desktop reports can be personalized in many different ways. Budget reports are used to highlight your planned amounts versus the actual spending in each account. It doesn't go into a breakdown transaction by transaction, but rather shows you a total for the accounts. To see what transactions have affected an account, you can double-click the line in the report to bring up a transaction report for it.
When it comes to purchase orders, these kinds of transactions won't show in this kind of report. A purchase order is a non-posting transaction that's simply an order you're sending out to your supplier. The dollar figure on a purchase order isn't allocated to any specific account because an exchange of money hasn't been recorded, like it would be for a payment.
I hope that helps explain it a bit. You can pull up an Open Purchase Orders report alongside your Actual vs Budget report to see them side-by-side. Exporting them to Excel would also give you the opportunity to manipulate them how you would like.
Here are a few articles about the topics I've mentioned above. Enjoy your day!