While new Public Charge rules will only go into effect for cases handled in the US postmarked after February 24, 2020 - there are already reports that the Department of State is delaying and denying cases for family members of US citizens and Legal Permanent Residents already approved by USCIS and now going through immigrant visa stamping.
This would appear to be inappropriate as the cases being denied and refused were all filed many months ago with USCIS, and should therefore be treated under the existing legal standard. However this does not appear to be the position that the Department of State is taking in this fast moving development since the Supreme Court recently lifted a lower court's injunction on the implementation of these new rules until legal challenges to the new rules have a chance to be reviewed by the lower courts.
Click here for a summary of what the new Trump Public Charge Rules look like...