how does mel newly awakened work with siphoned power

No — Empowered Mel does not boost Siphon Power. Siphon Power's only choice is the battlefield, and Mel's replacement effect keys off a unit the spell chooses, so nothing qualifies to be replaced. Enemy units there still just get −1 [M].

Mel's Empowered text reads "if a spell or ability you control would give −[S] to a unit it chooses, it gives an additional −1 [S]," and the Moonfall ruling (FAQ #11737) confirms that only the event on the unit actually chosen gets the extra −1 — other units hit by the same spell don't. Siphon Power chooses a battlefield, not a unit (FAQ #2524: it targets the battleground and doesn't target units), so no unit's −[M] event is eligible and the minimum-of-1 cap stays as printed.

Contrast that with Moonfall or Stupefy, where a unit is chosen — those do get the extra −1 (and inherit the "to a minimum of 1" cap, FAQ #11741). No official FAQ covers this exact pair, so this is my reading of Rule 370.1 plus the Moonfall precedent.