[peteeng]

Hi Mem - The power supplies go to motor drivers not direct to the motors. Drivers are very well controlled and are current limited so unlikely to be a problem on the electronics side. To lose a step the motor has to experience more back torque then the drive torque the motor & driver can supply. This can be mechanical friction, an object. acceleration or decel overloads, cutting overload etc .... Peter

[memphisjed]

The power supply is going to only put out so many amps. You have 4 motors drawing 4-5 amps each, as soon as the power supply reaches its capacity all motors will de-tune and not equally. Add to that as soon as one starts decel it is back driving voltage, lowering the voltage to other motors while still drawing amps.
once a stepper looses its cog they become very weak, the other motors will start absorbing any available amps. The reason it is able to catch cog again is it is being jump started by the other x axis motor dragging it.
Steppers that work in a coordinated motion really deserve a single power supply per motor.