I have and Uncle whose son has POA for him. When he asks him for money he wants to know why and what for.

Mickey, if the Power of Attorney now has access to his Dad's finances, that tells me that maybe, just maybe, his Dad is unable to do it himself. Do you know if that is the case?

I assume you are hearing about this money issue from your Uncle. How is his health? Does he have any memory issues? If yes, it could be that he is telling a "story" which is not unusual if he has dementia or Alzheimer.

To piggyback on Jeanne's answer, your uncle, if he is mentally competent, can revoke POA and appoint someone else in his stead.

The POA is to carry out the person's wishes. It is his money. It should not be withheld from him. I think your cousin should look up what a POA authorizes him to do and what he has no authority over.