PSUs are fairly cheap considering. you want to make sure you get enough wattage for the other components to run properly. I’m assuming since it’s a budget build for $800 a 650-700w should do just fine. But when in doubt get more wattage. A 900w seems a bit much for you without knowing your build specs. to sum up I’d get something name brand. seasonic, corsair, evga. 650+ W