The interest in the use of atmospheric-pressure plasma jets (APPJs) is constantly growing. APPJs offer various ranges for applications, such as wound healing, cancer treatment, and dental care. The complex plasma chemistry plays an important role in each of these fields but is often poorly understood. In this paper, the production of atomic oxygen in a radio frequency helium-oxygen plasma is investigated by means of a numerical simulation. A 1-D discharge of an atmospheric-pressure plasma jet is created with the plasma module of COMSOL Multiphysics, using a set of 25 reactions. Many 1-D simulations usually cannot estimate the power deposition in a correct way because of suspected arising losses, such as radiation and inefficiencies of the external circuit. In order to match the experimental power deposition of 13 W, high voltages (855 V) are required in the model. Such high voltages cause changes in the plasma characteristics like a switch in the glow mode. The impact of the voltage on the plasma is investigated by the comparison of a low-voltage (325 V) simulation, which matches the experimental oxygen production, and a high-voltage (855 V) simulation, which matches the experimental power deposition. Outcomes of this paper further support the idea that the power deposition measured in experiments is higher than the actual power deposition coupled to the plasma.