The Jenkins manager supports a custom text or YAML format of the plugin list as described [on their github page](https://github.com/jenkinsci/plugin-installation-manager-tool#plugin-input-format).

By default, Renovate gets the versions from the main [Jenkins update center](https://updates.jenkins.io/).

There are no strict filename rules, the convention is to name the file `plugins.txt` or `plugins.yaml`.