added Lighting

Check to see if you have 120 volt lights as well as the 12 volt DC. We have both and I installed a 4 foot track light with four 120 volt AC halogen spots. If by some chance you do not have 120 volt lights in the vicinity you want to upgrade, You can still install a set with a drop cord running down the wall and just plug it in to an outlet. There are covers made to keep a cord against the wall and out of the way for a neater installation. If you are a handyman, it is not a difficult job.
Russ

Ebay is another source for 12V lights.

Basically you can't make the wiring both 12 volt and 120 volts (or use the same wires). You will need to either buy lights that match the existing ones or run separate wires and separate power source for the new ones.

I suspect that the existing lights are 12 vdc. The Home Depot ones will be 120 vac.
You will need to get the new ones from someone that carries 12 vdc fixtures. Camping World is one such place.

Dunno.. all my lights are 12v

If you are tapping in to an existing 120V light for your 'wanted' 120V light, you can most certainly get them from Home Depot. Of course, they will only work when connected to shore.