Constant voltage power supplies are also know as LED drivers. They provide a stable 12V DC supply to LED bulbs and flexible LED strips, ensuring the life isn't reduced by using an incorrect supply.
This LED driver is a rated at a maximum of 40W (3.33A). It's a waterproof driver which is more suited to installing in damp conditions although they are also ideal as a general LED driver.
It's also small enough to be screwed to the underside of a kitchen cabinet and has mounting points to facilitate this.