Recent years have witnessed an extraordinary spurt in attention toward the wave-manipulating strategies revealed by phase-amplitude metasurfaces. Recently, it has been shown that, when two different phase-encoded metasurfaces responsible for doing separate missions are added together based on the superposition theorem, the mixed digital phase distribution will realize both missions at the same time. In this paper, via a semi-analytical procedure, we demonstrate that such a theorem is not necessarily valid when using phase-only metasurfaces or ignoring the element pattern functions. We introduce the concept of asymmetric spatial power divider (ASPD) with arbitrary power ratio levels in which modulating both amplitude and phase of the meta-atoms is inevitable to fully control the power intensity pattern of a reflective metasurface. Numerical simulations illustrate that the proposed ASPD designed by proper phase and amplitude distribution over the surface can directly generate a desired number of beams with predetermined orientations and power budgets. The C-shaped Pancharatnam-Berry meta-atoms locally realize the optimal phase and amplitude distribution in each case, and the good conformity between simulations and theoretical predictions verifies the presented formalism. A prototype of our ASPD designs is also fabricated and measured, and the experimental results corroborate well our numerical and semi-analytical predictions. Our findings not only offer possibilities to realize arbitrary spatial power dividers over subwavelength scale but also reveal an economical and simple alternative for a beamforming array antenna.