In this paper, we address the problem of synthesizing decentralized current controllers for grid-feeding converters of current-controlled distributed generation units (CDGUs) in dc microgrids (MGs). Notably, a plug-and-play (PnP) design procedure is proposed to achieve grid-feeding current tracking while preserving the collective MG stability. Through the presented control scheme, seamless addition/removal of each CDGU to/from the MG is ensured, with no need to update controllers of neighboring CDGUs and to know the information of the MG. At the mathematical level, the set of control coefficients guaranteeing the aforementioned features is explicitly characterized in terms of simple inequalities. The inequality set only depends on the local parameters. Moreover, the proof of the MG closed-loop stability exploits structured Lyapunov functions, the LaSalle invariance theorem and properties of graph Laplacians. Finally, theoretical results are validated by hardware-in-loop simulation tests.