What does the rectifier do on 1988 evinrude 48hp motor?

The rectifier changes AC current to DC current. This allows the remaining voltage generated by the Stator (alternator) to help recharge the starter battery. The AC voltage goes through the (power pack0 SCR switches / capacitors, and then to the 2ndary ignition coils to boost to 45,000 + volts then to the spark plug.