If I do NOT have primary healthcare here in the U.S., if I purchase one of the secondary coverage plans from a company that doesn't require primary coverage, does that secondary plan essentially become my primary plan?
my insurance company will cover 50%. will secondary insurance pick up the remaining
Correct, a policy that provides secondary coverage will cover for any eligible expenses that are not covered by your primary provider.
Which plans offer coverage without primary health coverage in the US?
Only the company GeoBlue mandates that you have primary health care in order to provide coverage. Some of the companies that sell annual medical policies will also require primary coverage for them to provide coverage.