If you already have Model Trains Simulator (Power Edition) for SCARM, you can then also select and download various locomotives and wagons from the Virtual Rolling Stock online database to use in the simulator.
However, almost each vehicle (or set of vehicles) comes in its own library and when you want to make a train containing various different cars, you should switch many times between the different libraries. That may be quite uncomfortable, but there is an easy way to change the grouping of the rolling stock vehicles in the selection panel.
To do that, start the simulator by use of “Extensions” > “Model Trains Simulator” menu command and then open the settings from “Tools” > “Settings” menu item. Scroll down the settings window until you reach the label “Rolling stock selection panel”. Below it there is a drop-down list that sets the grouping of the vehicles – open it and select “All together” as shown below:
Press OK button to close the settings window. Now you should see all downloaded and installed vehicles from all libraries in the rolling stock selection panel in 2D formation mode of the simulator.
You can also group the vehicles by types (locomotives & cars), countries/regions, railroads/operators or switch back the grouping by libraries. Note that the MTS options page in the settings is only visible when the MTS extension is started and running.
MTS Online help