A hub device includes an upstream port, multiple downstream ports, a first and a second sub-hub module, a data-format detector, a transaction translator, and a controller. The upstream port is coupled to a host device supporting a first and/or a second data format. Each downstream port is coupled to one of a plurality of slave devices supporting a first and/or a second data format. The first sub-hub module supports transmission of data in the first data format. The second sub-hub module supports transmission of data in the second data format. The data-format detector detects the data format supported by the host device and the slave devices. The transaction translator transforms the data format between the first data format and the second data format. The controller determines whether to control the transaction translator to perform data-format transformation.