"AGP 3.3" isn't correct terminology, that could be why you're having trouble getting the answers you need.
AGP comes in three flavours, 1.0, 2.0 and 3.0. some marketing genius decided to sell them as "2x", "4x" and "8x" respectively.
1.0 was 3.3V only, 2.0 slots offer 3.3V and 1.5V, 3.0 slots offer 1.5V and 0.8V but not 3.3V.
You have a 3.3V AGP 1.0 Card, so need a 1.0 or 2.0 slot.
The motherboard chipset determines the AGP standard. Also as mentioned the slots are keyed. If the card fits it *should* be electrically compatible. There are corner cases though where this isn't true. These basically only occur when pushing the limits, i.e. very new motherboard compared to your old card. A period correct or even one gen newer board is a safe bet.
The systems you link to are from the same time as the V3 and also have (3.3V) AGP 1.0 ("2x") Slots thanks to their i440BX chipset. This chipset is an excellent period correct choice for compatibility and performance.
That does not apply more broadly for these systems though. This is an era in which specifically Dell and (in some systems) Compaq used proprietary power supply pinouts. They may look like a regular 20 pin ATX connector, but hook an ATX PSU up and fireworks will ensue 😦
Given that the PSU is one of the commonest components to fail in old systems, this is an unwelcome complication if you're not well-versed in the matter.
Unless you have a strong sentimental reason to go for Dell or Compaq, for a beginner I'd recommend choosing a more standards-based system (i.e. basically anything from that era that isn't Dell or Compaq).
