Start with the isolation requirement
An autotransformer shares part of its winding between input and output and does not provide galvanic isolation. A double-wound transformer uses separate primary and secondary windings. If the equipment requires isolation between these circuits, an autotransformer is not an interchangeable alternative.
The same voltage can still require isolation
A 220V-to-220V transformer may still be useful when circuit separation is required. Selection must also consider the equipment grounding arrangement, protective measures and applicable requirements. Separate windings alone do not establish compliance with every safety requirement.
A practical comparison
Autotransformer: common winding connection, without galvanic isolation; potentially smaller under suitable conditions. Isolation transformer: separate windings for applications requiring circuit separation. Compare dimensions and cost only after rating, voltages and construction are defined.
What to include in your inquiry
Specify primary and secondary voltages, VA or kVA, phase and whether isolation is required. For a replacement, include the nameplate and terminal markings. Similar appearance does not establish electrical interchangeability.