The document introduces the features and performance of the 339 combined transformer (American box-type transformer), including reliable power supply, compact structure, fast and flexible installation, convenient operation, small size, etc. This product is widely used in industrial areas, residential communities, commercial centers, urban roads, high-rise buildings, and other places. Compared with the European box-type transformer, the American box-type transformer adopts an integrated design and has a smaller size. It has a fully sealed and insulated structure without the need for insulation distance, ensuring personal safety. At the same time, the product has the advantages of low loss, low noise, low temperature rise, strong overload capacity, short-circuit resistance, and strong impact resistance.