In past releases these may appeared that they were the same thing or almost the same thing as they were controlled by the same setup, also the terms encumbered, reserved were often interchangable used to mean both or either.   In Oracle Financials these are considered two distinct features.

Budgetary Control – keep track amounts of and determine if there is available funds within a given budget with Funds Available = Budget – Encumbrance – Actual

Encumbrance Accounting – the creation of accounting journals earlier in the the document cycle than with standard accrual (ie during PO/Req time instead of Receipt/Invoice)

You can have budgetary control without encumbrance accounting the Funds Available = Budget – Actual.  Also you can create encumbrance journals with out being subject to checking if funds are available, ie without budgetary control.

In R12 Encumbrance Accounting is controlled by SLA (SLAMs) and budgetary control is controlled by the setups defined in Summary Templates and Budget Organizations.  Budgetary Control does use the data created by SLA as input to determine funds availability, however you can suppress SLA journals from going to the general ledger.