The toriodal transformer is a TenPao TOU433020F0 for the 120V AC version, which outputs 14.7V.
Power supply has a Taiwan Semiconductor GBU805 bridge, and an International Rectifier IRFZ44n Power MOSFET. The big capacitor is a 25V 33000 uF made by Aishi. There is a thermal protection on the heatsink, labelled RT1. If your varistor gets blown, the part number is 275L40B.
Bose Companion 3 Amplifier
The amplifier IC is TDA7560. Datasheet specifies it as a “QUAD BRIDGE CAR RADIO AMPLIFIER PLUS HSD”. The TDA7560 is a BCD (Bipolar / CMOS / DMOS) technology class AB Audio Power Amplifier in Flexiwatt 25 package designed for high power car radio.
Power output ranges from 4x30W / 4 ohm @ 14.4V with 10% THD, to 4x77W / 2 ohm MAX. For a THD of 1%, power output is around 23W for 4 ohm, or 43W for a 2 ohm load. More specifications can be found in the TDA7560 datasheet here.