Dependabot private registries

When I configure dependabot to use a private registry it stops using a default public registry for my package-ecosystem (I’m using nuget).
In dependabot logs I see
before configuring registries: section: GET https://api-v2v3search-0.nuget.org:443/query?...
after configuring registries: section: only GET https://<my private registry>/query?...

How do I make both (private registry and default public, nuget.org in my case) working together?