Social Security Supplemental is a different program. Its paid out of general taxes.
Social Security is paid out of work contributions = FICA. Its a compulsory retirement savings program.
They are two very different elements of Social Security.
No, it is not a retirement savings program. Your contributions do not belong to you. A person could pay into the system for 50 years and not receive a dime except for a small burial allowance. It is a Ponzi scheme.