What is the meaning of "Timtza Yadcha l'Chol Oyvecha"?
Rashi: Every Makah of Your hand that You have, bring it on Your enemies.
Radak: [Hashem tells David,] your hand will suffice for you; you will not need help. This is like "Yadav Rav Lo" (Devarim 33:7). This is because "ha'Melech Bote'ach ba'Shem" (verse 8).
Malbim: After this vision, David fought great wars with Pelishtim, Mo'av, Aram and Amon, and killed two thirds of Mo'av. When your left hand will suffice [to defeat] your enemies, and your right hand will suffice for your haters
Why does it say "Yemincha Timtza Son'echa"?
Radak #1: The matter is repeated in different words. It is like l'Son'echa; the prefix Lamed in l'Chol [Oyvecha] applies also to Son'echa. Timtza is to suffice, like "u'Matza Lahem" (Bamidbar 11:22).
Radak #2: Your hand will find your haters; they will not be able to escape you.