Your performa isnt ADC, it is a larger form of VGA called DB-15, which was phased out with the Beige G3 in 1998. From then on VGA was the standard on B&W G3s and Early G4s. ADC started shipping in 2001 and stopped shipping in 2004(possibly '05, but Im pretty sure '04) with PowerMac G5s.
A good set of rules is as follows:
PowerMac G4s below 466Mhz and 500Mhz models shipped with a card with DVI-D and VGA.
PowerMac G4s above 466Mhz excl. 500Mhz machines shipped with a card with ADC and VGA or in the very last G4s (Dual 867Mhz, 1Ghz, 1.25Ghz and Dual 1.42Ghz models), a card with DVI (normal DVI) and ADC. The only machine that doesnt quite follow this is a specialised G4 QuickSilver which could have an option for a card with 1DVI and 1 ADC.