Total guess but probably 12 volt , and at least 3 amp to be safe. For example this long string of LEDs is 12V 40 Watt, which is about 3.3 amps.

Then you have the cable top size to figure out.

You could get one of these adjustable supplies and probably find something that works.

But as everyone else has mentioned, check the back for details. You might even need to look up a part number for a LED controller or something like that. Good luck.