A compatible end device will provide signals (basically resistor values) that will tell the USB-PD adapter what the output voltage should be and the maximum output current. Programmable output voltages can be 5 volts, 9 volts, 12 volts, 15 volts, or 20 volts. Maximum power is available at the 20 V output level, as the adapters are specified by their maximum current ratings. For example, a 60 watts rated power adapter is limited to 3 Amps (20 volts times 3 Amps equals 60 watts). At 5 volts output, the available output power is therefore 15 Watts (5 Volts times 3 amps equals 15 Watts).