Superman One Million is Kal Kent, a descendant of Superman from the future who due to some 5d imp DNA and the energy of the Super sun has some additional powers. He's herald+ level, but not quite Skyfather.
Superman Prime One Million is our Superman who's over 850,000 years old and has been residing in the sun for the last 100,000 years. The Super Sun that helps make Kal Kent so strong is, in part, a result of him. Also, just for kicks, he has the last Green Lantern ring too, which he used to crush Solaris the Tyrant Sun's body. He's majorly cosmic.
Aside from the powers he obtained from the Source, a 100,000+ year sun dip, AND the last GL ring, Superman Prime M* literally IS the 'battery' which powers the entire Superman Dynasty. Without his energies (in the form of the Super Sun) constantly feeding them, the members of the SD are all but powerless.
This is like pitting Galactus against Surfer.
__________________
"I am tired of Earth. These people.
I am tired of being caught in the tangle of their lives."
And in DC, what is found at the very edge of time and space? The Source Wall (and subsequently, the Source itself.)
So yeah, while it may not have been directly stated that his powers came from the Source, it's perfectly logical to assume such, based on the information that was provided. Imo.
__________________
"I am tired of Earth. These people.
I am tired of being caught in the tangle of their lives."