In general I believe there are only two types that work:
1) The water based ones which are relatively new on the market - they just use water and sonic vibrator disc which atomises the water into vapour which is then blown out the funnel using a small PC fan. Upside is that they use water and are cold so no heat whatsoever and that current consumption id quite low, in the region of 1amp. They are also quite easy to make using nebulisers from e-bay. Downside is that they can be quite large and need a decent amount of headroom for the mist to form and they also typically work on 24 volts. In itself that is not a problem as you can cheaply procure a rectifier which jumps the voltage to 24 volts but this then doubles the current consumption to 2amps.
2) Oil based which typically muse some hot coil of wire wrapped round a wick to generate the heat and vaporise the smoke oil - now there is a lot of old misconception with these as the modern ones don't use oil at all but fog fluid of some description. This is non toxic and non hazardous and allegedly non flammable (mixture of de-mineralised water, glycerine and a specific type of glycol). Now with these the current consumption can typically be higher in the region of 3amps to 5amps. The downside is the current consumption and candidly following a number of experiments I have found the non-blameable fog fluid is flammable under certain conditions (An entirely different subject).
Some people use various oil mixtures (baby oil being one) but in my experience the unburnt oil coats the hot element which eventually caused overheating and burns the coil out.
Overall with the nebuliser based units I find the smoke doesn't stay very long and is rapidly dispersed. With the fog fluid ones the smoke hangs around much more - neither system in my experience leave any residue on the model.
Both units actually produce fog as opposed to smoke so its not possible to introduce a black dye to make black smoke because you are trying to make black fog which just doesn't exist!
Both systems actually work in the same way by atomising a liquid, one by ultrasonic vibration and the other by heat - the fluid is transformed into tiny droplets which refract the light and we get a "white" fog effect.
All food for thoughts
Cheers
Geoff