<p>Nonlinear energy sinks have received extensive research attention due to their merits, including broadband vibration absorption and lightweight design. However, the research considering gravity requires further refinement. This study presents an asymmetric stiffness nonlinear energy sink (ASNES) to address wide-range excitation parameters in the vertical direction for expanding the potential applications of NES-type devices. Initially, the ASNES structure, along with its experimental apparatus, where the ASNES is attached to a linear primary oscillator (PO), is introduced. Then, the vibration absorption performance of the ASNES is assessed using both sweep and fixed-frequency tests. Experimental results demonstrate that the ASNES achieves a maximum vibration absorption ratio of 88% in the sweep test and 85% in the fixed-frequency test. Subsequently, the dynamic equation of the PO-ASNES system is formulated to facilitate analysis of the dynamic characteristics of the ASNES, which is validated by comparing experimental and simulation results. Subsequently, using the equation, the effects of the ASNES on the experimentally studied PO under higher excitation accelerations and on three other POs with various resonance frequencies are numerically predicted to more comprehensively demonstrate the overall capability of the ASNES. It is found that the ASNES can be applied to primary oscillators with different resonant frequencies across a wide range of excitation accelerations. Finally, the vibration absorption performance of the ASNES is compared with that of a cubic NES, and a parametric study of the ASNES is conducted.</p>