Power Of Attorney& Trustees

What is the name of your state? Calif.
Can a power of attorney transfer bank accounts and cars into their name? Also what are the duties of a trustee?

Did the transfers occur before or after the death of the decedent?

The person is still alive, but in jail, and it was done now.

You still have not provided enough details to make a valid determination of your situation. You need to be talking to a business law attorney or a probate attorney about this--there are steps you can take to try to get the power of attorney cancelled/revoked, that is if the person who signed it agrees to do so.