The best way to cross-reference two circular connectors is to have your original part number. For example TE part number HD10-9-96P . If you scroll down the page to product attributes you can select attributes that you absolutely need by clicking the box on the right-hand side. If you need an exact match you can always select all at the top of the column. I have highlighted the sections below for easy identification:
If you don’t have the part number, circular connectors usually have part markings. For example, Souriau-Sunbank part number UTS1JC124S has marked on the shell as seen here:
This part marking gives us two clues because it’s the name of the series. Trim Trio is only manufactured by Souriau-Sunbank. If you have this connector your next steps would be to search Trim Trio on our website from there you can select what type of connector this is a housing and then filter by the number of positions.
TE part number HDP26-18-20SN has markings on the internal grommet as seen here:
This part marking gives us two clues as well: Deutsch and HDR26-18-20SN, which is the manufacturer and the part number.
Here is a reference on what different types of circular connectors look like: https://www.digikey.com/en/resources/connectors/circular-connectors just in case there are no part markings or the connector has been damaged.