I am designing an ultralow noise 5V/3A SMPS.

On the DC side, I see the ground (DC) is earthed (chassis ground) using a direct connection 0 ohm or using a Y capacitor. What are the differences between them and whats best for low noise on DC output?

On the positive side (DC) I also see that sometimes it's earthed (chassis ground) using a Y capacitor. Is it recommended to make this connection (if our goal is low noise on DC output)? Is 330 pF enough as a value for the Y cap?