Adam Clarke on Psalms 103:20

Bless the Lord, ye his angels - Every person who has a sense of God's goodness to his soul feels his own powers inadequate to the praise which he ought to offer; and therefore naturally calls upon the holiest of men, and the supreme angels, to assist him in this work.

That excel in strength - Some take גברי כה gibborey coach the mighty in strength, for another class of the hierarchy, - they that do his commandments, hearkening to his words; and consider them to be that order of beings who are particularly employed in operations among and for the children of men; probably such as are called powers in the New Testament.