If I have POA, do I need a DPOA to take control of finances for my mother who has dementia?

What exactly do you mean by "POA" vs DPOA"? A DPOA normally includes a list of specific permissions which the writer allows the agent to act on. The list can be fairly long to cover practically any situation that might be encountered when taking over the affairs of another person.

If by "POA" you are referring to a Health Care Proxy, it covers a different set of circumstances.