The tenth amendment does not conflict with the supremacy clause but simply duplicates it. It says that states and the people have all the powers that are not prohibited by the constitution itself which sets up the constitution as the supreme law of the land. Any law passed by the federal government is invalid by default since it can’t take away any power from the people or the states since the tenth amendment states that only the constitution can prohibit those particular powers and if the ‘powers not delegated’ didn’t exist every federal law would be unconstitutional.
The tenth allows for one exception to this rule which is powers delegated to the federal government since the constitutional supremacy that the tenth amendment confirms only exist for powers not delegated to the federal government. Any law passed using powers not delegated to the federal government is superseded by the constitution’s supreme authority since the tenth amendment only refers powers not delegated to the federal government.
This also establishes a basis for why laws are unconstitutional since laws made by the powers of the federal government can’t be invalidated by the constitution’s supreme authority because laws made with powers not given to it are second to the constitution’s authority. The tenth amendment then says that those particular things that those laws attempt to prohibit that have been made outside of the property delegated powers of the federal government can only be prohibited by the constitution itself.
This automatically invalidates those laws since only the constitution can restrict people and states in those areas and if we assume that the tenth amendment is the actual basis for finding laws unconstitutional in Marbury v. Madison then it means that the tenth amendment is the basis for judicial review. There is reason to suspect that this was the basis for judicial review since Chief Justice Marshall said “or conformably to the Constitution, disregarding the law, the Court must determine which of these conflicting rules governs the case”.
Clearly he understood that the constitution is the supreme law and all federal law is lower to it and the tenth amendment says that only the constitution can limit powers that have been retained by the people or the states. This rule only applies to powers not given to the federal government which is why federal laws can be struck down when they are not made in with powers delegated to it. In other words, only the constitution can limit the powers retained by the people or the states only when those powers have not been delegated to the federal government but power delegated to the federal government are immune from the constitution’s supreme authority. The tenth amendment establishes that only the constitution can limit the actions of the people or the states except when those laws are made in pursuance of the constitution or uses a power delegated to it (same thing).
This means that judicial review is quite limited for the state laws since only laws that go against the specific prohibitions stated in the constitution can be declared unconstitutional and powers not delegated to the federal government are. It can not declare a law unconstitutional simply because it conflicts with federal law but only because it conflicts with one of the specific things that states are prohibited from doing in the constitution. The federal government has no authority over the states and has very little direct authority over the people since only the constitution has that level of authority over them.