Okay not being able to actually see the power supply output, you could have an issue. Yes that is a 12 power supply but is it an AC supply or DC supply? If the power supply is merely a 120VAC reduced to 12VAC, then not all your LEDs are going to light. So even with the proper attachment cord and wired into the panel switch, you may not get all the LEDs to come on. It really depends on the type power supply they went with. If it is an AC output, then alternately the LEDs will light during their part of the AC cycle. But since it would happen so fast, it would look like all of them are lite at the same time. So applying a 12 DC voltage to them, only half will light. Really depends on how there are wired from the factory. Just saying! JMHO!