Smooth output feedback stabilization for nonlinear systems with time-varying powers**This work was supported by the National Chiao Tung University Short Term Research Scholarship funded by The Ministry of Education under Taiwan’s 2015 Global Networking Talent Plan; and the Ministry of Science and Technology (MOST), Taipei, under grants NSC 102-2221-E-009-063-, MOST 103-2221- E-009-055-, and MOST 104-2221-E-009-075-.