Three is the ask for the vast majority of psych programs. One really needs to be psych and 2 is better, many people say their program wants one non-psych, but is isn't uniform. Other specialties want one from a chair or one from a PD, but this is very rare in psych. ERAS does flag letters from chairs. As above, there are a few programs that want 4 letters. In this case, I would think that any less than 2 psych would be bad and any more than 3 would be bad.