In order to do both, you need to be sure you have version 5.8.30 of FanTestic or later. 

In all versions of FanTestic before version 5.8.30,  if you plugged a DM32 into a computer USB to give it power (instead of plugging into the wall adapter) FanTestic would assume you also wanted to use USB Serial connection for control.  FanTestic made this assumption even if the gauge was also connected to the computer over Ethernet (via the Network cable or via WiFi). 

In all versions starting with 5.8.30, FanTestic discovers gauges connected via Ethernet first, so it can ignore the same gauge also found on USB Serial. 

This change allows users to have their DM32 connected for control via Ethernet but also connect the DM32 to the computer USB port for power (if it is more convenient than connecting to a wall outlet).  Retrotec recommends that users use Ethernet connection rather than USB for controlling the DM32.