Most ATS manufacturers we see build their own contactor assembly (Power Panel, PP) and we work on them all: ABB (Zenith), ASCO, Onan, Cummins, Kohler, Russelectric, Generac, Eaton, Westinghouse, GE Zenith, etc.
Except for some cases where above a curtain rating (usually 1200A) they use another manufacturers part. Like in the case of the attached pic. It is a 2000A Cummins ATS with a ABB (Zenith) PP. Cummins also uses ASCO P Panels above a certain amp rating. Kohler and Cummins have the license to private label ABB ATS's to sell as their own.
Also attached is an ABB ATS nameplate with the UL label listing the complete unit. As others have mentioned, I think you would be hard pressed to find a PP with its own label.