Yealink EXP50 User Manual page 19

If you connect two expansion modules, connect the USB jack on the prior expansion module
and the mini USB jack on the next expansion module using another supplied cable. Connecting
two expansion modules on a single host phone is shown as below:
Power is automatically transferred from the host phone to the expansion module(s) upon
Note
connection. If you want to use more than one expansion modules on a single phone, you need to
connect an additional Yealink power adapter (5V/2A) to any one of the expansion modules.
The power adapter should be purchase separately.
To attach the stand of the expansion module:
Getting Started
11