Voice conversion systems can transform audio to mimic another speaker's voice, thereby attacking speaker verification systems. However, ongoing studies on source speaker verification are hindered by limited data availability and methodological constraints. In this paper, we generate a large-scale converted speech database and train a batch of baseline systems based on the MFA-Conformer architecture to promote the source speaker verification task. In addition, we introduce a related task called conversion method recognition. An adapter-based multi-task learning approach is employed to achieve effective conversion method recognition without compromising source speaker verification performance. Additionally, we investigate and effectively address the open-set conversion method recognition problem through the implementation of an open-set nearest neighbor approach.