Steam humidifiers are very good - they have two carbon rods that are submerged in the water, and the minerals in the water conduct the electricity between them and this heats the water, and it produces steam. No dust gets into the air, and it warms the room rather than chilling it.

If the steam is too slow, then add a little salt to the water and it steams faster. Believe it or not but pure water is an electrical insulator.

You need to scrape the rods - the minerals build up on them. Oh, and the other great thing about this design is when the water runs out - it shuts off. And there are no moving parts. They are inexpensive - like under $20 for a 2 gallon model.

I have not measured how much they consume, but I don't think it is very much.

I have never heard of this type.. Sounds pretty neat. A little like some kind of battery.. ;)
Got a link?

That sounds like the vicks humidifier I got. It suggests adding salt the steam better.

It sounds like how the whole house humidifiers work, the ones connected to your HVAC system.
Never seen a portable version