Does the Commerce clause stop states like CA and NY from joining to require certain environmental standards when it comes to power supply/sales of goods?
It means that the federal government can preempt/void a state law, but nothing currently prohibits. Most commerce today is actually regulated at the state level by the Uniform Commercial Code that states individually adopt.
The commerce clause means that the federal government can prevent a farmer from growing subsistence crops. Basically that the federal government has no limitation except where explicitly prohibited.