Is that outlet grounded?

Grounded outlets were not required until the mid 70s. Your home may have been built with two-prong outlets, and a previous well-intentioned homeowner may have replaced the old two-prong outlets with newer three-prong version. However, unless he installed a ground wire, it is still a non-grounded outlet. Outlet testers are an inexpensive way to see if the outlet is wired properly. A tester can be purchased at most hardware and home centers.

Grounded Outlet Diagram Figure(A) and Figure (B)
If your outlet is not properly grounded or if it is an older two-prong outlet (Figure A) it would be preferable to have an electrician run a ground wire to the outlet.

Electronic equipment must be plugged directly into the surge suppressor with the surge suppressor plugged directly into a grounded wall outlet (Figure B) for full warranty coverage.