The ornamental design for a portable swingadaptor, as shown and described.
The portable swing adaptor is a simple to use, portable, adjustable and machine washable fabric device that adapts most average-sized playground swings to a more supportive swing for toddlers and small children.
FIG. 1 is a front perspective view of the portable swing adaptor; and,
FIG. 2 is a rear perspective view of the portable swing adaptor.