1. A system comprising: a DC-to-DC converter to convert a voltage on an input node to a voltage on an output node; a switching device coupled in series between a DC supply node and the input node, the switching device configured to selectively isolate the DC supply node from the input node; and a controller coupled to the input node and to the switching device, the controller configured to: apply a test current to the input node; enable the switching device to be switched from a non-conductive state to a conductive state if a voltage on the input node is above a threshold while the test current is applied to the input node; and restrict the switching device from being switched from the non-conductive state to the conductive state if the voltage on the input node is below the threshold while the test current is applied to the input node.