Sidecars are great things but are very tricky to handle. You are correct that the RAW Power sidecars are not designed to be read by other apps. They could certainly be revised to make them readable but that wouldn’t actually solve the problem. I believe you want to edit an image in RAW Power and then somehow get the image to appear properly in Photo Supreme. There are two ways for that to happen:
1) Photo Supreme can read RAW Power adjustments AND faithfully reproduce them.
2) Photo Supreme extracts a full-size JPEG from RAW Power and displays that.
#1 is not practical – Photo Supreme would need a copy of the RAW Power editing engine, which of course it doesn’t have.
#2 is possible but it would need to know how to get the full-size JPEG. In the case of RAW Power, it’s stored next to the sidecar.