The power system monitoring problem asks for as few as possible measurement devices to be put in an electric power system. The problem has a graph theory model involving power dominating set in graphs. The concept of -power domination, first introduced by Chang et al. (Discret Appl Math 160:1691-1698, 2012), is a common generalization of domination and power domination. In this paper, we present a linear-time algorithm for -power domination in block graphs.