A wireless power system (WPS) has a wireless power transmitter (WPT) that appraises an input power available to a power inverter from one or more input power sources. The WPT comprises the power inverter that wirelessly transmits power to a wireless power receiver (WCR) of the WPS, and a power appraiser circuit (PAC). The PAC ascertains maximum input power available to the power inverter from the input power sources. The PAC includes a variable load connected to a path carrying the input power to the power inverter or one or more input pins that receive power ratings of the input power sources that indicate available maximum input power from the input power sources. The ascertaining of maximum input power available to the power inverter from the input power sources appraises the input power available to the power inverter. The WCR receives information representing maximum power deliverable by the WPT.