Keep in mind that the official integration of TP-Link to Smartthings can exist parallel, but it is separate from the SmartApp.
Both the SmartApp and the Device Handler (DH) need to be installed through the IDE, and if both the official TP-Link integration and the SmartApp are installed, each device will appear 2 times.
The HS300 is relatively new, and probably need some modification in the DH, similar to what I did for the KP115: TP Link Kasa Devices with new official integration (July 2019): reviews needed - #164 by ernie
However, as the HS300 is a multi-socket device, not sure if the DH in its current form will correctly report the HS300 device capabilities. Making this another reason to push TP-Link to update their integration into Smartthings with the missing Energy Monitoring (EM) capabilities.