Summit 550 W power supply units (PSUs) are available with either front-to-back or back-to-front airflow. If you install two PSUs, both must have the same airflow direction.
Summit 450 W power supplies are compatible with Summit X480 series switches and with Summit X670 series switches that have front-to-back ventilation airflow.
Summit 550 W power supplies are compatible with Summit X670, X670-G2, and X770 series switches. They are available in versions for switches with either front-to-back or back-to-front airflow.
Note
You cannot combine power supplies of different wattages in the same switch.