Is supplemental health insurance enough

Probably not. Supplemental health insurance is designed to fill holes not covered by major medical insurance plans: deductibles, co-pays, co-insurance, policy limitations, income replacement, and non medical expenses such extra travel, lodging expenses, etc.

Major medical insurance is designed to cover your primary need - catastrophic losses associated with a sickness or injury. Supplemental insurance should not be viewed as a replacement to major medical coverage.