How to stabilize a linear power supply using Ltspice?

[Datguy123]

Hi, I am building a linear power supply. I am unsure if my method of analyzing the open-loop gain on LTspice is correct because the magnitudes on the bode plot did not seem right (with a FB of 6.8k/750, the low-frequency gain should be around 20dB). I have sufficient phase margin for this DC operating point, but once I apply voltage with V3, the circuit starts to oscillate. Does that mean that I need to attain the bode plots of many DC operating points to ensure the supply is always stable?