I have a DVI and VGA output monitor. I have a mini displayport adapter for both but need to use another adaptor to go to Thunderbolt 3. Not working.

If I understand your question, you have an external display with DVI and VGA input, you have a new(er) Mac with only Thunderbolt 3 / USB-C ports, and you want to connect the display.

In that case, yes – you need to buy a new adapter, either a USB-C-to-DVI or USB-C-to-VGA adapter. I'd recommend using the DVI input.

In general, you need to make the jump from computer output to display input in at most ONE adapter. With few exceptions, you can not "stack" adapters.

This is because the adapter at the computer end has to ask the computer to re-arrange the output signal for the upcoming conversion. If you "stack" adapters, that request is lost.