This is a W2 series transformer manufactured by KS-AD which is used as a power supply in applications such as lighting, audio amplifiers and voltage converters. The 4_CZ_K_125/RYGB/M describes the transformer details, with 4 referring to the number of secondary winding taps, CZ referring to the connection style, K indicating the neck length, 125 referring to the power rating in VA, RYGB identifying the colours of the wires, with Red (R) signaling primary, Yellow (Y), Green (G), and Blue (B) signalling the secondary, and M indicating that the transformer is encapsulated.