I just added a power outlet on the panel behind the center console of my '08 Prerunner DCSB 4.0. I used an add-a-circuit & plugged it into the original fuse location of the front 2 outlets. I had previously done the "power all the time mod" so now all 3 of my outlets have constant power. As per the instructions, one of the 2 slots on the add-a-circuit is for the original fuse in that location & the other slot is to fuse the accessory that is being installed.
It also says not to use more than 10 amps but the person who installed my rear view mirror with built in compass used the fuse that powers the 4WD, which I don't have, but it has a 20 amp fuse. The rear view mirror fuse is either 4 or 5 amps.