Extension problem with portserver II rack model

We use three entities (64 ports), an extension and now the power does not seem sufficient. The last extension the entity loses electricity.
There are more environments in operations by us and in each one of them the same problem.

Must an extension be used with the entity a separate power supply?

Yes. It appears the port usage is beyond what the base PortServer II unit can power. You will want to add an external power supply for the last module in the chain.