Transformers are necessary to supply voltage to pond lights. Most of our pond LED lights run on a safe low voltage. The correct voltage is needed for pond lights, otherwise damage could occur to the LEDs. That's why a transformer is necessary to maintain the voltage level and to avoid any problems.
Aqua Gardening has several pond lighting transformers of various wattages. You may check the Aquascape Pond Lighting Transformer, PondMAX Jack Plug to Transformer Adapter, and PondMAX Light to Transformer Plug Adapter. All these products are housed in weatherproof cases and are safe to handle. These transformers will allow you to plug in a splitter or light directly. Be sure to choose a transformer with enough power to supply the lights you are trying to run.