I have found the the Midi Solutions Power Adaptor to be indispensable when using other Midi Solutions midi processing units, such as Event Processors, Mergers, Thru's etc in a chain.
The Midi Solutions Power Adaptor will power up to 20 Midi Solutions devices.
The Power Adaptors become necessary, since many electronic organs, and other electronic musical instruments, have insufficient power available from the midi_out socket on the instrument.
In some instances the LED on the Midi Solutions box lights up, but the unit does not function.
This is because the LED requires such a small amount of power in comparison to the other electronics in the box.
The Midi Solutions Power Adaptor will power up to 20 Midi Solutions Devices.
Midi Solutions publish, on_line, a long list of electronic organs and other devices which insufficient power on the midi_out.
See Midi Solutions - FAQ.