I am working on a proposal for a DB and 401k PSP carve out. All employees are highly compensated anesthesiologists. The combined plans are top heavy. Do the participants in the 401k PSP need to get a 3% top heavy minimum or a higher top heavy minimum since there is a DB plan. There are no overlapping participants.

Do you mean Highly Compensated Employees? Are they also Key Employees?

If they all are Key Employees, then they don't need to receive any Top Heavy benefits

That's true, legally. The plan language must require TH minimums only to non-keys, rather than all employees.

If there are non-key employees who participate only in the 401k plan, I believe they only need a 3% TH minimum.

However, if they are in the DB plan, you need to pick the method that works best.
5% DC
2% DB
2% DB with floor offset of PS account
Comparable benefit to 2% DB.

If they are getting good benefits from the DB in any event, then TH should be trivial in the DB plan.

Also, the doctors need to tell you if they are employed through their professional corp even if they don't own a part of the medical group. If so, then they need to adopt into the plan, and they are key employees.