Smoke machines have a heating element, a pump and sometimes a fan for smoke blowing and/or fan for cooling powersupply or other internals.
Pumps and motors only like 'pure sinewave' inverters. These create 'smooth' AC from the batteries, while 'stepped' AC in cheaper inverters don't maintain a changing magnetic field in the motors so the surge and stop ~400 times a second.
I don't know which type of inverter the Vagabonds use. If they do indeed produce 'pure sine', then I'd say the item isn't capable of maintaining the required current.
Check the current rating on the smoke machine.
Compare the current capability of the Vagabond.
I'd suggest you might still be in trouble if you're trying to use the strobes (which probably suck as much current as you can give it) with the fog machine together.
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