The Providence & Worcester, pre-merger, ran a regular program of excursion trains, and being primarily a freight operator didn’t have any power that provided HEP power. So they purchased one of Amtrak’s heater cars – ex-AMTK #456, rebuilt from an E9B – to provide hotel power to those trains.
After the merger, new HEP equipped class DP2 electro-diesels supplanted X688, so it ended up moving first west of Owego, then up into Canada for operation on the TdM & LT&L’s dieselised route segments.