The current is unstable when the power supply is switched using an Solid-state Relay. Why is this?

When an attempt is made to turn the Solid-state Relay ON, voltage is applied to the Solid-state Relay, and the Solid-state Relay tries to turn ON, but near point A where there is no current flow the ON status cannot be maintained, so the Solid-state Relay turns OFF and then turns ON when the charge current starts to flow at point B.

Similarly, the Solid-state Relay moves from OFF to ON at point C. If there is a delay in the Solid-state Relay turning ON at point B, the capacitor will no be sufficiently charged, and when the Solid-state Relay turns on at point C it will try to charge the amount insufficient at point B, which will result in a large current flowing. The current is unstable because this process is repeated at points D and E.

As a measure to stabilize the current, connect a bleeder resistor that constantly passes current in parallel with the power supply to keep the Solid-state Relay ON.

Bleeder Resistance