The cable drops the 5V USB voltage down to roughly 3.2v this is very close to the supply of 2 AA batteries (1.6v each = 3.2v)

The lead has a Male USB 2.0 plug one end and a 2.5mm straight DC barrel jack the other. 

They are 1.2m in total length

This cable is the same for Game Boy Color, Game Boy Pocket and Game Boy Light consoles

Power your consoles from any USB or USB power bank with this Cable