Out of curiosity .....

I have some waterfall lights 31V DC. Two wires go to a control box that sends the chase effect to the various strands.
Could the DMX2-24 be utilised power it, and to turn it on and off.
I know it is designed for AC strings, and surely works by switching positive and negative rapidly to use both channels of that string. If you only commanded, say, channel 1 on, and left channel 2 off, wouldn't that effectively be a DC supply?

You could put a 3A diode in series with channel one (anode to controller, cathode to +ve of connected load) so that at worst it would output pulsed DC and not reverse polarity whatever you're feeding.

If they are the 3 wire type of waterfall lights, I'm pretty sure they're multiplexed. That or one of the strings is alternating polarity LEDs and the 3rd line is the last leds.

How many wires from the controller out to the lights?
The DMX2-24 toggles the polarity at 100Hz or whatever frequency it is that I last made it. Having 1 channel on and the other off actually provides a 0-31V square wave of 50% duty cycle at 100Hz.