This is a slightly annoying trophy to grind out. It will take you a lot longer than you think. However it'll help you on the way to
I found the best way to do this is to take Ryu into Versus mode against a Zangief on the easiest difficulty, with 7 rounds, and throw light shoryuken (forward, down, down-forward). You want to try to avoid killing zangief with them. If you jump back the shoryuken may not hit him. Once you've hit super on your EX bar, you'll want to beat Zangief down til he's with in an inch of his life (I found the life bar should be below two of the four victory icons under the bar experiment if you want.) Then throw your super move (for Ryu it's the motion of the hadoken twice and any single punch attack, I used Light) and that should start the animation for the super and hopefully kill the enemy.
You will get a flashy screen if this kills him and an S instead of a V (though if you perfected the round it'll be a P, though Super combo finish will appear on the left side of the screen as the finish is happening)
Get 50 of these and you are done with this trophy.