Romex is a brand name. The type of non-metallic cable for direct burial is UF, the type for dry locations is NM-B. UF is intended to be used with the ends and splices properly sealed or in dry locations. While some code provision might be violated by using the NM-B as installed buried for 24 volt (or less), if it was my property I would use it since it is already installed. If the outer jacket is not damaged, it probably will last for at least 10 years if the cut ends are properly sealed. The voltage involved presents no hazard to most individuals. No doubt others will have a decidedly different perspective.

OK, everyone got me sufficiently paranoid to contact Juno. The tech rep responded as such to my question about using a dimmer designed for a magnetic transformer on a dedicated outlet for a magnetic transformer: "Electrically that arrangement would work. Since you state that the outlet is located in a remote location, and presumably will be dedicated to only provide dimmable power for the T550N transformer you should be OK. The only reservation I have about this type of setup, is the possibility of some other electrical device being plugged into a wall outlet wired off a dimmer. It might be a good idea to use a single receptacle instead of a duplex to minimize the chance of this happening. Perhaps even labeling the outlet "for low voltage lighting only" or something of that nature as an added precaution. You will have to install a cord and plug on the transformer. If you have not ordered the T550N already, you can order it with a 6 foot cord and plug option. You would order the transformer as catalog# T550N-BL-CP6. Otherwise you can attach your own cordset." I apoligize for not getting all the facts beforehand. Would those who recommended trashing the existing systems or felt there was imminent danger of fire consider this sufficient or are there still logical objections?

Where all the other bulbs are a normal intensity, this sounds more like a bad connection to me. It it were from too much of a load, all the bulbs should be dimmer than normal...not just one. Just out of curiosity, you do have the same type bulb in this light, right?

What ever you do, do not us irrigation wire nuts. Don't know where you are located but if you are near a large city or in one there should be a Ewing Irrigation Store close. Ewing1.com. They sell 3-M DBRY splice kits meant for higher amps than irrigation connectors. You have less than 50 watts on your 12/2 wire now and you are talking about adding another 15 watts for a total of less than 70 watts... ... ... not an issue what so ever unless you are planning on running those two lights over to your neighbors yard or you live on 10 or more acres and want to put them at the top of your driveway. Is your transformer multi-tap? If so put the 12/2 on the 15 volt tap that way you will have enough oomph to drive the last LED. The industry standard for 12 volt LEDs is an operating range of 9 to 15 volts. Less than 9 volts and the LED will not come on, more than 15 volts and you will burn out the circuit that drives the LED. As always take any advise with a grain of salt and read the instructions that came with the light fixtures and through the salt over your left shoulder. Hope that helps.