A multi-level voltage regulator system/method providing discrete regulation of a DC-DC intermediate bus converter (IBC) output voltage (Vout) is disclosed. The disclosed system/method allows IBC Vout to be regulated in discrete steps during periods where IBC input voltage (Vin) falls below nominal operating values. Rather than shutting down or degrading IBC Vout in an unpredictable non-linear fashion based on IBC input/loading, IBC Vout is regulated in fixed discrete steps, allowing IBC-connected point-of-load (POL) converters to obtain stable power input that is well-defined over IBC Vin. IBC operating parameters may define multi-dimensional operational state spaces of IBC Vout regulation that ensure optimum power flow to attached POLs while maintaining operational stability within the IBC regulator. Instabilities in IBC/POL performance across variations in IBC Vin, load transients, POL loading, and environmental variables may be prevented using Vin voltage step hysteresis.