For more details about assembly,please check below link.
https://www.printables.com/model/883817-unoriginal-prusa-heated-drybox
Benefits:

The heating system features a 200W PTC heating element in combination with two fans to blow hot air through the drybox. The heating system is located under the top panel of the drybox ensuring that the drybox still holds up to 6 spools with a diameter of 21 cm. Using the 2mm polycarbonate panels and with all 6 spools the heating system can reach temperatures of up to 45 degrees Celsius or 113 degrees Fahrenheit in 15 minutes making it perfect for drying multiple spools of PLA at the same time*. It can also reach temperatures of up to 65 degrees making it suitable for PETG**.

The (Un)original Prusa Heated Drybox is a heating add-on for the (Un)original Prusa Drybox. The heating add-on gives the extra functionality of drying wet filaments and even constantly heating to reduce the relative humidity. The add-on is available for both the CLASSIC and SLIM Edition of the drybox and is a good project for anyone who wants to learn how to solder and work with electronics.

Note: Please check the option you choose, the cheaper one is without PSU.