Harry's later Force Rings, the ones stacked on each other? He can trigger just a few, or all of them at the same time. To me, this is modeled best by thinking of them as having multiple uses, or a high frequency count. But when he triggers them all at the same time, he's using every single frequency use at the same time for a really big attack.
Harry seems to fire off a bunch of the rings at once at least once per book when he really needs it (i.e., the plot demands it).
I try to make the game work as much like the books as is reasonable, so if the plot of your scenario demands it and it doesn't destroy your scene, you should consider it if you think it makes sense in your campaign.
The problem is that once you let players get away with something like this, they may try to do it all the time. You still have a several avenues of recourse.
The easiest way to regulate this is to require they spend a fate point for each extra charge used. That gives an inherent cost that limits abuse. Basically, any time a character wants to do something that Harry does in the books that isn't covered directly by the rules, you can charge them a fate chip.
You could require that the player take a stunt that allows "supercharging" items this way. If you want to limit this, you can also charge a fate point every time they do it.
Then are purely mechanical solutions: The player has to roll a to-hit, and your NPCs have fate chips to spend to increase their defensive rolls. That means the player can blow all the charges on the rings and
miss completely, wasting all those charges. If this happens a few times when the player is abusing this capability, they should get the message.
Then, there are campaign-based solutions: over the long haul, that wizard will get a reputation for pulling this trick, and NPCs will eventually be prepared for it. That's a big part of Harry's shtick in the books -- he knows his opponents' tendencies and plans for them with all sorts of gimmicks. All it takes is one opponent who has a specially prepared mirror gizmo or tricky spell maneuver to turn all that power back on the caster, and he will be more selective about cutting loose.
Finally, using that much energy at once can have dire consequences, especially if those attacks are aimed at mortals, or if mortals get caught in the crossfire. If your wizard PC blows out the side of a building and it crushes a busfull of kiddies on a field trip, the White Council may have a thing or two to say.
So, you as the GM don't have to say "no" to a player. You can have the NPCs or the story line show him the error of his ways in-game.
