You can replace internal power supplies as needed while the switch is operating ("hot swapping"). However, if you are changing the airflow direction of the internal power supplies and fan modules, you must power down the switch.
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.
To replace one or both AC internal power supplies in an 8720 switch, follow the steps in Installing a 750 W Internal AC Power Supply.
To replace one or both DC internal power supplies in an 8720 switch, follow the steps in Installing a 750 W Internal DC Power Supply.