The ornamental design for a foldable supportadapter, as shown and described.
FIG. 1 is a right side elevational view of a foldable support adapter in accordance with our design shown in a first, folded position, with the left side elevational view being a mirror image thereof;
FIG. 2 is a top plan view, with the bottom view being a mirror image thereof;
FIG. 3 is a front elevational view thereof, with the rear elevational view being a mirror image thereof;
FIG. 4 is a top, front, left perspective view thereof;
FIG. 5 is a right side elevational view thereof in the unfolded position, with the left side elevational view in the unfolded position being identical thereto;
FIG. 6 is a top plan view thereof in the unfolded position, with the bottom plan view being identical thereto;
FIG. 7 is a front elevational view thereof in the unfolded position, with the rear elevational view being identical thereto; and,
FIG. 8 is a top, front, left perspective view thereof in the unfolded postion.