Power Supply model for Oscillator

Hi! I am trying to simulate a power supply model for an oscillator. I use transient analysis to study the behavior of various parameters.I have an inductor and resistor connected in series to the power supply's positive and negative terminal which is in turn connected to the oscillator. The issue is that when I place the ground terminal(gnd) connected the oscillator vss the oscillator oscillates perfectly fine but when I move the gnd terminal so that it is connected to the power supply's negative terminal the oscillator doesn't oscillate at all. I am just wondering what could be the reasons for this. Since its a ring oscillator the initial conditions are set appropriately or may be it has something to do with how the initial estimates are calculated.