I have developed power loss protection for SSDs in the past. You also need to give an early warning "power failed" signal to the controller to dump its internal

I have developed power loss protection for SSDs in the past. You also need to give an early warning "power failed" signal to the controller to dump its internal buffers and state. Power loss can be very challenging to get robust especially if the controller uses clever algorithms at runtime to get better performance because recovering the drive state from sudden power loss is more difficult. That is why I think the Intel 520 controller has so many problems because they are using a SandForce controller which was known to use no external DRAM and compression algorithms which just complicates things.