A power apparatus applied in an SST structure includes a first AC-to-DC conversion unit, a first DC bus, an isolated transformer, a DC-to-AC conversion unit, a second AC-to-DC conversion unit, and a second DC bus. The first AC-to-DC conversion unit has a first bridge arm and a second bridge arm. The first DC bus provides a first DC voltage. The isolated transformer has a primary side and a secondary side. The DC-to-AC conversion unit has a third bridge arm and a fourth bridge arm. The second AC-to-DC conversion unit has a fifth bridge arm and a sixth bridge arm. The second DC bus provides a second DC voltage.