Methods and devices for increasing power delivery efficiency of wireless power transfer systems are disclosed. A wireless power transfer system may include a power transmitter system and a power receiver system. The power transmitter system may comprise a power amplifier, a power transmitter, a controller, and a sensing circuit. The power amplifier may be configured to receive an input power. The power transmitter system may include a transmitter-side coil configured to wirelessly couple to a receiver-side coil of the power receiver system. The controller may be configured to set a voltage and a frequency of the power transmitter system based on output power information of the power receiver system to increase wireless power delivery efficiency of the wireless power transfer system. The sensing circuit may be configured to determine the output power information of the power receiver system.