Camera rig with multiple AC transformers
Devices have not used actual transformers for 10 or more years. Instead, they use switching power supplies. This has made the plug pack smaller and cheaper. What you can't get around is power. 

Your 10 plug packs are capable of 148 Wats of power. That may not be how much the cameras are actually consuming. What you need to understand is that if you replace the 10 with one, the one will be about the size of the 10 combined (roughly). 

What you'll need is a supply that is preset to or adjusted to 7.4V and that is capable of 20 or more amps. If the supply is adjustable you'll need some way to hold the adjustment so that it doesn't accidentally get bumped. Then you'll need a wiring harness that connects all the cameras to the power supply. This either means you build something from scratch or cut the wires off the 10 you have and wire them together.