Simple Spells per Encounter Add On

I've loved the idea of Spells per Encounter since seeing their inkling in Cooldown Magic from Unearthe Arcana, Maneuvers & Stances from Bo9S & Jedi Mind Tricks from the previews of Star Wars Saga Ed.

This is simple way to add something similar to existing Arcane & Divine Spellcasters.
NOTE: the very best system I've seen for this is in Spellbound: Channeler from Crafty Games for Spycraft 2.0. If you have an interest in this BUY IT.

Basically at the beginning of an encounter, the DM either draws a Playing Card from a Deck or rolls 2D6 for the Mana Class(MC) of the Encounter. If using Playing Cards, Aces are = to 11. If you draw a Face Card, draw an additional card until you get a number card or an Ace. Then add the number of Face Cards to the value of the Number Card.

This is the number of extra Spell Slots any Spellcaster has access to for that Encounter.
For purposes of Spell Slots, 0-Level spells = 1 Spell Slot but allow you 3 additional castings of 0-Level spells.

So if I was an 8th Level Wizard, my max Spell Level is 4. If the MC is 6, I can add an 1-4th level spell, & either 2-1st level spells or 1-2nd level spell or 1-1st level spell & 1-0 level spell (for 3-0 level spells)