This article explains the Fan combinations and Airflow types on Dell EMC Networking S4112T-ON/S4112F-ON model switches..
Fan combinations
AC PSU
DC PSU
Normal Airflow
Reverse Airflow
There are four fan combinations available in S4112
These FAN units are factory installed and shipped based on order placed by the customer upon their installation requirement.
This image represents the I/O Panel with AC power supply.
This image represents the I/O Panel with DC power supply.