Dynamic reactive power support capacity of new energy units is generally weak, and with the increase of new energy generation, the system’s voltage support capacity declines, making voltage stability issue more prominent. Existing studies lack quantitative evaluation methods for determining the maximum deliverable new energy output under voltage stability constraints. To address this gap, this paper first derives an analytical expression for the theoretical maximum active power output of new energy sources considering static voltage stability criteria. The resulting formulation explicitly quantifies the relationship between the theoretical maximum active power and factors such as system short-circuit ratio, impedance ratio, and reactive power compensation capacity. A calculation method for the minimum reactive power compensation capacity to meet active power generation demands is also proposed. The correctness and effectiveness of the proposed method are then validated using continuous power flow analysis based on numerical modeling. Finally, using impedance-based analysis on a detailed time-domain model with full control loops, this paper preliminarily verifies the correlation between voltage stability levels and wideband oscillation risk. The research findings provide reference for rapid and accurate assessment of new energy delivery margins, determination of required reactive compensation capacity, and evaluation of the stability level of new energy delivery systems.