Can a guardian, through the court, override my durable power of attorney?

Yes.

If someone is petitioning the court for guardianship over your POA then it will be decided by the judge in the case.
The person or entity (sometimes it can be the state or a NH) who's petitioning for guardianship has to have grounds for why they believe you are inadequate as the POA, and they will have to prove that you're mismanaging funds and not looking after the person's best interests.
Often times nursing homes try to petition for guardianship when a POA refuses to give them full access to all the money and assets. I had this happen with my parent. I was an effective POA. The bills were all paid in a timely manner and the estate was processed and all business was being taken care of.
The NH petitioned the court because they wanted direct access to bank accounts and I refused. It was my right to pay the bill monthly as I saw fit. Their other reason for petitioning was because I treated their bill the same as every other. They were not the only bill my parent owed money on.
Whoever is trying to override your POA must show proof that you are not adequately performing the duties of the POA. If you are then you'll be fine.

godisreal1: Guardianship generally overrides power of attorney because guardianship is a court order.

Many DPOA actually have a nomination of conservator. My father’s does. It specifically states that he wishes I be his guardian if the court petitions one. My father’s attorney said that unless I was proven to commit elder abuse or proven to be unfit to serve, it would be highly unlikely a judge appoint one from the court. I asked because I live on the opposite coast and was curious what would happen if say my dad was found wandering or someone called APS on him.

Ditto what others have said. It also depends on what kind of PoA you have: medical and/or financial. If you have both, an eldercare attorney can help sort things out for you.

Yes, Absolutely. A guardian whether appointed through a court or applied for and appointed through a judge will be the one to make all of the decisions from financial to placement. They will be in charge. A conservator or guardian always trumps POA. Often a guardian is appointed by the court when there is some question about a POA's actions, as to whether they are correctly doing their fiduciary duty. They are also appointed by a court in the case of people fighting over guardianship.

Was there already a court hearing? Did you attend with you DPOA document?

Yes. A guardian involved actually cancels any DPOAs.