Emmien

Actually I am not sure. I think they use a SMPSU, but I know that they often get the timings from the AC power frequency.

Are you sure, I don't think this is true. All christmas lights I have seen for 5+ years have a little switching regulator in the power supply box. A lot of strings (Especially cheaper ones) do now have those hideous plug, PSU and multi-function controller things, and only two wires leaving the plug to the lights. The lights are wired with each LED being the opposite polarity to the previous. They do the effects with PWM, but when you have both sets on, there is a slight flicker as the polarity has to be swapped very fast to keep them on.

I use some store bought lights in my Christmas lights display. Majority of low voltage Christmas lights use a 24VAC transformer, and have a rectifier which converts to 31VDC in the controller box. The plug you have must have the controller built in. I use Alan Hanson 2801DC15s. They take WS2801 data and control from5 to 35 volts. Problem is they come from Australia, but only takes a week or two. I use 30v power supplies. The supplied ones are unreliable and voltage fluctuates. I got them from China, but you can find them here intended for use with printers.

That device should work. Most desks that use floppy have ordinary computer drives, with a floppy connector and 4 pin floppy power connector. Just unscrew the old one, insert a USB emulator one, and it should work straight away!