The API Model 500VPR is powered externally by a tri-polar power supply and is designed to accept API standard format 5.25" X 1.5" modules. The 500VPR is internally wired for PIN 2 hot, and comes with the API L200PS. The input/output jacks are both XLRs. The 500VPR can hold up to ten API modules. API makes several modules to fit this rack, including the 550A, 550b, 560, 525, and 512c.