This power supply is a compatible replacement for Bestec part number ATX-300-12EB3 S4 power supplies. If you own a Bestec part number ATX-300-12EB3 S4 this ATX-300-12EB3 power supply will fit without modification. We also offer this power supply upgrade that will replace your Bestec part number ATX-300-12EB3 S4 power supply.