This has come up a number of times over the decades. Currently, as I see it, there are three ways to do this:
(1) If there is a dimension on the drawing that has the format you wish, just reference that dimension in the table cell.
(2) Type the text into the cell and then format the superscript and subscript bits with the corresponding text formatting selections in the ribbon.
(3) Bring up the Text->Text Editor window and type the text in with the archaic Pro/E "markup" codes: "{0:9.45}{1:@+-0.2093@#}{2:@--0.3153@#}{3:@-@#}"
Here's a thorough discussion from long ago:
Old text tips discussion