The Universal Power Inlet System, or UPIS, is a method of providing universal attachment of 3 different types of electrical power systems into the input circuitry of a Power Distribution Unit, or PDU. This method allows use of either fixed or detachable power cord options permitting the PDU to be powered by any of the following types of electrical power sources: 3-Phase Delta, 3-Phase Star (or Wye) and Single-Phase. This method also describes a way to uniquely identify the specific power system the mentioned PDU is currently attached to. The method also optionally allows derivation of supplementary information about the electrical power system such as current capacity, or ampacity, of the power cord being used. All this information can be used for capacity monitoring and reporting as well as protection of PDU circuitry and power cords.