Aprilaire 4010 Humidifier Transformer The Aprilaire 4010 Humidifier Transformer is designed for use with Aprilaire humidifiers 400, 550, 550A, 558, 560, 560A, 568 amp; 600 Aprilaire 24v humidifier transformer. Input 120 vac, output 24v, 10 watt (10 va). Mounts in a utility box Humidifier Transformer For Models 400, 550, 550A, 558, 560, 560A, 568, 600