The output DC voltage of a center-tapped rectifier is half that of a bridge rectifier when using the same transformer primary-to-secondary ratio. This is because the center-tapped configuration only rectifies half of the total secondary voltage during each half cycle, while the bridge rectifier utilizes the full secondary voltage for rectification in both half cycles. If a center-tapped rectifier had a transformer with a secondary voltage twice that of the bridge rectifier, the output would still be half, excluding diode voltage drops. The difference in output voltage is fundamentally due to the number of diodes and the voltage utilized in each configuration. Understanding these principles is crucial for designing efficient rectifier circuits.