Oh perhaps they are mains powered LEDs. A 240v AC voltage uses a 1:1 or 1:2 transformer and is then rectified to high voltage DC using a bridge rectifier, then the LEDs are chained in series. The thing with this is that you can then have dozens of LEDs in series and only have one resistor. It's efficient and safe provided the rope is well insulated. It won't, however ever work off a 12v fan controller.
I'm guessing that black box contains a transformer, a rectifier array and a capacitor or two. If not and it is a filter then the electronic gubbins will be towards the start of the LED rope.