From the AM enhancement tree.
Arcane Supremacy [2 AP] (ML 5, Char 12, 30 AP)
On offensive spell cast: 10% chance of: +25% Spell Critical Chance, +100% Spell Critical Damage
12 sec duration, 90 sec cooldown
This looks really cool but how much does it actually add?
Lets say on average it takes 10 sec to make it proc (thats somewhat generous with a 10% chance) meaning its active 12 sec every 100 sec for a 12% uptime.
If you have no spell crit chance without it the +25% would add 25% more damage total but since you are likely to have another 25% crit chance at least from other source these 25% to base adds 20% total (150% / 125% = 1.2).
If you had zero crit damage otherwise the +100% would double your crit damage. Since you are likely to have some crit damage from other sources as well lets say 50% then these +100% to base is actually 67% (250% / 150% = 1.67). I am unsure about the exact sources of spell crit damage available after U19 but +50% sounds on the low side to me.
In total this means that Arcane Supremacy roughly adds 12% * 20% * 67% = 1.6% to your total damage on average.
Maybe its just me but this seems a bit underwhelmning. I might think that the 100% crit damage should be +200% instead.
Compare this to adding +30 USP from tier 2 in the AoV FvS tree. Even with 600 spell power another 30 is a raw increase of 5% to all spell damage - and an even larger increase with lower than 600 spell power. Admittingly this cost 3ap while Arcane Supremany only cost 2ap but its much easier to accesss.
Obviously one can simply take both in some cases but for my WF Wiz/FvS/Mnk there are simply so many great enhancements to pick from that its hard to spent 30ap in the AM tree to reach Arcane Supremacy if its not better than 1.6% increase to overall spell damage.