Totally, utterly a fraudulent power.
The Constitution specifically says that no state may tax the exports of another state.
Do you smoke? Guess what... your state ignores this provision.
The Constitution means whatever the hell they feel it means at whatever time to serve their purpose, they have basically decided to ignore it.
It is my firm belief that a repeal of the 17th amendment would go a long way to restoring a lot of problems.
Because then you would have state governments getting into knockdown dragout fights in the senate and reversing/preventing a lot of crap going on.