How do we add connections to more data sources in an existing gateway?
How can we tell what data sources a gateway provides connections to?
Do you want to create connections to several on-premises data sources?
Currently, gateway supports the following data sources, SQL Server, SharePoint, Oracle, Informix, Filesystem, DB2.
To add connections to more data sources, just follow the similar steps showed in this doc and select the existing gateway when you are asked to Choose a gateway.
Besides, to know what data sources a gateway is connecting to, please go to web.powerapps.com>Data>Gateways>Connections.
Hope it could be your reference.