A header assembly includes a header housing having a cavity configured to receive a receptacle connector therein. The header housing has at least one cartridge latch in the cavity. A signal header cartridge is received in the cavity and locked in the header housing by the at least one cartridge latch. The signal header cartridge has a plurality of signal contacts extending between mating portions and mounting portions that extend from the signal header cartridge. A power header cartridge is received in the cavity and locked in the header housing by the at least one cartridge latch. The power header cartridge has a plurality of power contacts extending between mating portions and mounting portions that extend from the power header cartridge.