Will it work, yes, if you jumper the green to a black the PSU will turn on, then tie all the yellow wires (+12V) and black wires together, it will run the amp.
However, it will not run it very well nor will the PSU last all that long.
1) The amp, I'm assuming to power subs, will draw large sums of power at random intervals, wish causes strain on the PSU which were designs for more sustained loads.
2) The PSU is designed to be loaded on all its rails 3.3V/5V and the 12V rail so it will work but its not the best for it and may damage the PSU.
3) The PSU probably doesn't have enough power on the 12V rail to fully power the amp, thus the amp might draw too much current from the psu and damage it.
I've done it before, I've also killed a psu before doing it.
Other options/solutions include: Using a cap/battery to distribute the draw from the PSU and try using multiple PSUs either in series (jumper 3.3 or 5v in series) or in parallel to lessen the power draw on the 12v rails.