For a given transformer the maximum output voltage available from a full-wave bridge rectifier circuit will be:

In a full-wave centre-tap rectifier, the circuit relies on a centre tap to act as a common ground, meaning the load only ever sees half of the secondary winding's voltage at any given time (from one end to the centre tap). A full-wave bridge rectifier uses four diodes to route current such that the load receives the full voltage across the entire secondary winding, from end to end, during both halves of the cycle. Because the bridge rectifier utilizes the full end-to-end secondary voltage rather than just half of it, its maximum output voltage is exactly double that of a centre-tap rectifier connected to the exact same transformer.