so the deal with the fans running at half speed is true but it depends how you wire them they are electronics yeah it is a little bit confusing but here is a diagram
okay it is with speakers but same concept when you wire in a series you are sharing the current between 2 fans so for a 12v adapter each fan will get 6v and run half speed.
When you wire parallel for some reason don't ask me why or how the current is kept constant at 12v for both fans
it is an electronics principle that is used a lot for led's and well all electronics lol so i hope that this helps someone