Look up hhoconnection on YouTube and watch Mike's videos; I posted a few bellow. He also has his own website hhoconnection. Another informative site is hho4free. This is where I started out before reaching this forum. Mike has a bunch of videos that are informative to get beginners started.
Here is a couple links to help answer your questions but I think that the 2 lower links best relate to your question having to do with Volts and size of plates.
The video that you posted is an example of a Wet Cell. This video is about the difference between Dry and Wet Cells
http://www.youtube.com/watch?v=gQOxWXRsLB4
Here is a video with tips for building an efficient Dry Cell
http://www.youtube.com/watch?v=OmXHhVh_nkY
This is about Volts and Neutral plates in a Dry Cell
http://www.youtube.com/watch?v=lDjyIvza6Yc
This video is about the formula you use, based on the size of your plates, to determine how many Amps you can feed your cell before over using it.
http://www.youtube.com/watch?v=QtlVJdrtbAM
Typically an efficient 12v dry cell will produce 1Liter Per Minute of HHO for every 15~18 Amps
The best 120v dry cell available, that I know of, will produce 1 LPM of HHO for every 138 Watts. The same inventor has a 12v Dry Cell that will produce 1/2 LPM for every 96 Watts
Volts X Amps = Watts
I hope this helps you