The statement is made under solemn interrogation before the high priest and council. Jesus' identity is therefore at the center of the judicial proceeding.
'The Blessed' and 'Power' are reverential ways of referring to God, making the heavenly placement of the Son of Man especially striking.
Psalm 110:1 seats David's Lord at the LORD's right hand. Daniel 7:13-14 presents the Son of Man coming with clouds and receiving everlasting universal dominion.
Jesus combines these two major enthronement passages and applies them to himself.
The high priest asks whether Jesus is the Christ, the Son of the Blessed. Jesus answers, 'I am,' and immediately explains the future revelation of his identity through Psalm 110 and Daniel 7 imagery.
The prisoner before the council claims that he will be revealed as the enthroned and cloud-coming Son of Man.
The words 'I am' should not carry the argument by themselves; ordinary Greek usage permits that response to the high priest's question.
The far stronger evidence is the scriptural claim that follows. Jesus places himself at God's right hand and assumes Daniel's heavenly Son-of-Man role, provoking an immediate blasphemy charge.
The high priest tears his garments, declares that Jesus has spoken blasphemy, and the council condemns him as deserving death.