At 12 volts 10 amps though 100 plates in series would make no gas at all (0.12v per cell/pair). You need a minimum of 1.20 volts per cell/pair to make gas and that will not be measurable but visible. 1.75 volts per cell does make measurable gas but unless the reactor is very efficient does not compare with 1.97 to 2.3 volts per cell/pair.
Now in your 100 plate reactor, if you ran the plates parallel -+-+- etc you would boil the water almost instantly at 12v and 10 amps per cell/pair.....well very quickly anyway and blow a fuse or something faster so nothing would happen unless you had a huge rectifier etc. LOL What are you trying to do?