Well, if the built-ins are relatively high (over 6' say), I'd do away with the whole lamp cord/cord cap/cheap extension cord setup I see in photo 3, and install a receptacle in the wall just above the built-installation to plug new fixtures into (if the new ones are setup like that). Or optionally, hardwire the new fixtures into a 1900 box set on top of the built-ins. I'd also like to know where those existing fixtures are plugged into ... Looks like something the cabinet builder may have rigged up, probably burying an outlet in the process. Don't really know from your pictures, just speculating based on experience.