I boil the distilled water. Place electrodes in and keep the heat up. Tried a cool one at 7.5v. took ages but turned out a very light tea colour so happy with that.
I have to be careful not to overcook it when using the heat method. Usually I stop about 10 mins before I think it will turn.
Been using an old Uniross variable voltage adjuster but the voltage is all over the place often +4
I have just found a constant voltage adapter constant at 12volts in my box of tricks.