Is there no other power adapter outlet in the back?
only one in the front and the usb plug in the upper glove compartment?
any suggestion to add more usb/power?

 

You are correct.

The easy way to add more power is to buy a lighter plug multi-adapter strip somewhere to plug everything in. So long as you aren't trying to power anything that needs a lot of power, you'll be fine—phone chargers, GPSs, etc.

If you want to permanently install an additional socket, it's fairly straightforward to wire one in. You could splice the existing wire, or find some other source of power. If you splice the wire to the existing lighter socket, you are of course still limited to the 10A maximum total current.

The USB socket isn't really meant for charging, and may not be able to charge every device (or at least charge them at all rapidly). It's rather meant to connect a phone or thumb drive to the radio for music playback. If you use a thumb drive, be aware that it may on rare occasions mess up the file system on the drive, so keep a backup—at least my Fit does that every once in awhile. Maybe it's just a slight incompatibility with my thumb drive.