The Orbitron is a compact electrostatic–magnetic confinement device that employs a radial electric field and an axial magnetic field to trap charged particles. In this study, its confinement characteristics and power balance were investigated using an ordinary differential equation-based trajectory model and two-dimensional axisymmetric particle-in-cell simulations under two representative prototype configurations. The results indicate that ions possessing initial azimuthal energy are primarily confined by the cathode-induced radial electric field gradient, whereas electrons are trapped through the cross-field (E × B) configuration formed by the coupled radial electric and axial magnetic fields. Under combined electron–ion injection, a quasi-neutral plasma is established, temporarily exceeding the conventional space-charge limit and exhibiting significantly enhanced confinement relative to single-species operation. The injected electrons further reinforce the inward-directed electric field gradient near the cathode center, effectively increasing the charge-holding capacity of the potential well. However, the plasma density remains well below fusion-relevant levels, and long-term operation is limited by field distortion and end losses. A power balance analysis further indicates that in weak-field, Coulomb collisions dominate the energy dissipation and the resulting fusion gain factor is approximately Q ≈ 0.6. In contrast, under strong-field conditions, although plasma energy and fusion power increase substantially, cyclotron radiation rapidly becomes the dominant loss channel, reducing the net gain to Q ≈ 0.134. These results demonstrate that while the Orbitron can overcome traditional space-charge limitations, insufficient plasma density and severe radiative losses remain the principal barriers to achieving net fusion gain.