A cooling apparatus is provided, which includes: a thermal conductor to cool a heat-dissipating component(s) of an electronics enclosure, the enclosure including an air inlet side through which airflow ingresses. The thermal conductor includes a first conductor portion coupled to the heat-dissipating component(s), and a second conductor portion positioned along the enclosure's air inlet side. The apparatus further includes one or more air-cooled heat sinks coupled to the second conductor portion to facilitate transfer of heat from the second conductor portion to the airflow ingressing into the enclosure, and one or more thermoelectric devices coupled to at least one of the first or second conductor portions to selectively provide auxiliary cooling. A controller controls operation of the thermoelectric device(s) and selectively switches operation of the cooling apparatus between an active cooling mode, where the thermoelectric device(s) is active, and a passive cooling mode, where the thermoelectric device is inactive.