when you install and turn on a second power supply on a catalyst 4500 series switch, it provides approximately one-half of the required power to the system. if one power supply fails, the other power supply immediately assumes full power to maintain uninterrupted system operation.

    load sharing works only when both power supplies in the chassis are the same type.

    when you install a redundant power supply, load sharing and fault tolerance are enabled automatically; no additional software configuration is required.