Assalaamu alaykum. I read that even if your father never helped raise you nor spent on you and stayed away out of his own choice, you must still obey him, can he just show up out of the blue and take some of your wealth, as the hadith says that the child's wealth is his father's, and can he take what he needs? Please, I need a full answer about the case in which the father has never been in his child's life.

All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.

There is no doubt that the son has rights over his father as per the sharee'ah. The father is obliged to provide for his young children who have no wealth to spend therefrom, take care of them, and provide them with good upbringing. If a father neglects this duty for no valid excuse, then he bears a sin for that. Allaah, The Exalted, says (what means): {O you who have believed, protect yourselves and your families from a Fire whose fuel is people and stones...} [Quran 66:6]

Ibn ʻUmar narrated that the Prophet said, "...the man is a guardian and responsible for his family..." [Al-Bukhari and Muslim]

ʻAbdullaah ibn ʻUmar reported that the Prophet said, "It is sufficient sin for a person to neglect his dependents." [Abu Daawood]

However, no matter how neglectful a father is of the rights of his children over him, this does not waive the religious obligation of dutifulness towards the father. Allaah enjoins dutifulness towards the parents even if they are non-Muslims who are trying to lead their child astray. Allaah, The Exalted, says (what means): {But if they endeavor to make you associate with Me that of which you have no knowledge, do not obey them but accompany them in (this) world with appropriate kindness and follow the way of those who turn back to Me (in repentance). Then to Me will be your return, and I will inform you about what you used to do.} [Quran 31:15]

Al-Bukhari allocated a chapter in his book Al-Adab Al-Mufrad entitled 'Chapter: Dutifulness to Parents, even if they are unjust.' He cited the following report, "Ibn ʻAbbaas said, 'If any Muslim obeys Allaah regarding his Muslim parents, Allaah will open two gates to Paradise for him. If there is only one parent, then one gate will be opened. If one of them is angry, then Allaah will not be pleased with him until that parent is pleased with him.' He was asked, 'Even if they wrong him?' He replied, 'Even if they wrong him.'" [Al-Bukhari] 

For more benefit, please refer to fataawa 82254 and 87019.

Despite the refined status of the parents in Islam, the father has no right to take whatever he wishes of his son's wealth whenever he wishes. The hadeeth to which you have referred in the question is not intended as a general rule with no limits. The scholars underlined the limits governing the right of the father in this regard in faaatwa 1569 and 89942. The son is enjoined to help his father financially whenever he can, regardless of whether the father is needy or not, so as to earn his pleasure and accordingly obtain happiness in the worldly life and the Hereafter. ʻAbdullaah ibn ʻAmr narrated that the Prophet said, "The pleasure of the Lord lies in the pleasure of the parent, and the anger of the Lord lies in the anger of the parent." [At-Tirmithi]

Allaah knows best.