Zalman ZM500-RS PSU Preview
 

The new series of power supplies recently released by Zalman ha a “RS” suffix in its name which stands for “Resonant Switching”. Compared to Two-Forward Switching, the more advanced Resonant Switching minimizes “switching loss” reduces heat generation, and operates more efficiently by eliminating the need for an output inductor leading to outstanding stability and reliability.
http://www.testseek.com/labs/reviews...rs-psu/?p=2511