GreggCM :
The subject power unit is in an Alien MJ12 Desktop 7550A system.
For the Tyan Thunder K8WE server motherboard that is in the Alienware MJ-12 7550a, Tyan had a power supply recommendation list of five PSUs:
Enermax EG651AX-VH
I-Star Computer Co. Ltd. TC-500R8A [24+8+4 pin, 500w, 1+1 redundant]
PC Power and Cooling Turbo-Cool 850 SSI
SilverStonetek Co., Ltd. ST-65ZF
Zippy Technology Corp. HP2-6460P
They're all discontinued
Like most of the power supplies from around that time period they had a combined output power on the +5V & +3.3V rails of around 200 Watts.
Most modern power supplies now have a combined output power on the +5V & +3.3V rails of around 130 Watts.
Do you still require Floppy Diskette Drive power connectors? If yes, how many? They're disappearing with a lot of the new power supplies now and only a 4-pin Molex to FDD adapter is being included.
I don't see any devices/components in your system that are going to draw so heavily from the +5V and +3.3V rails that any modern power supply won't be able to handle it.
The examples that @rolli59 gave is a good starting point.