You can replace internal power supplies as needed while the switch is operating ("hot swapping").
All installed power supplies must have the same airflow direction (front-to-back or back-to-front) and must also match the airflow direction of the fan modules.
If the power supply module has a red tab, the airflow is front-to-back.
If the power supply module has a blue tab, the airflow is back-to-front.
To replace one or both AC internal power supplies in an 8520 Series switch, follow the steps in Install a 750 W Internal AC Power Supply.
To replace one or both DC internal power supplies in an 8520 Series switch, follow the steps in Install a 750 W Internal DC Power Supply.