Add the cashews to a high-powered blender, along with the vinegar, lemon juice, water, and oil. Blend on medium or high speed, scraping down the sides as you go, until relatively smooth and creamy. Add the nutritional yeast, garlic powder, onion powder, and salt, and blend again until well incorporated and completely smooth. If you have a large blender container, like a 64 ounce jar, this will take several minutes, as you will need to scrape down several times, as there is very little liquid.