I have a 2003 Oldsmobile Alero 3.4 V6.
I was told that I had to replace my alternator with a Bosch brand because no other brands will work.
Is this true? Do I only have one option and I must get the Bosch because no other brand will work?
In fact, it looks like the OEM alternator is made by Delphi.
The website linked also lists the models that share this alternator (model 130D763):
Make Model Engine Model Years CHEVROLET CAMARO 3.8L V6 1996-1999 CHEVROLET CAVALIER 2.2L L4 BI-FUEL 1999 2002 CHEVROLET CAVALIER 2.2L L4 CNG 2001 2001 CHEVROLET CAVALIER 2.2L L4 OHV 1999 2002 CHEVROLET CAVALIER 2.4L L4 1996 2002 CHEVROLET MALIBU 2.4L L4 1997 1999 CHEVROLET MALIBU 3.1L V6 1997 1999 CHEVROLET MONTE CARLO 3.8L V6 1998 1998 OLDSMOBILE ALERO 3.4L V6 1999 2003 OLDSMOBILE BRAVADA 4.3L V6 1998 2000 OLDSMOBILE CUTLASS 3.1L V6 1997 1999 PONTIAC GRAND AM 2.4L L4 1996 1998 PONTIAC GRAND AM 3.4L V6 1999 2003 PONTIAC GRAND PRIX 3.8L V6 1998 1998 PONTIAC GRAND PRIX 3.8L V6 Supercharged 1998 1998 PONTIAC SUNFIRE 2.2L L4 OHV 1999 2002 PONTIAC SUNFIRE 2.4L L4 1996 1998 PONTIAC SUNFIRE 2.4L L4 1999 2002
In @Chris's comment, he says it was the guy at the auto parts store who told him that the only alternator he could get was a Bosch brand.
This leads me to believe that what has gotten lost in this question is that the auto parts store was simply out of stock of other brands.
Auto parts stores are not a warehouse and only keep a few of each item on hand. They can usually ship in your needed part within two days for free.