A power transmitter for wireless power transfer includes a control and communications unit, an inverter circuit, a coil, and a shielding. The control and communications unit is configured to provide power control signals to control a power level of a power signal configured for transmission to a power receiver, provide a power request to an external power supply, determine if a power signal at the coil is compliant with the power request, and, if the power signal at the coil is compliant with the power request, continue to operate for wireless power transmission. The coil is configured to transmit the power signal to a power receiver. The shielding comprises a ferrite core.