I've used many transparent PNG's so far but when I upload them on After Effects, it shows up with a white background for some reason. I made sure that the picture was PNG many times but it won't work. Added a screenshot below.
That looks like they weren't correctly saved from PS in the first place and the trasnsparency grid has been baked in. You might want to review your procedures over there. Perhaps it's an issue with hardware acceleration, perhaps it's a problem with your save settings. As a test impoirt the actual PSD file or export your artwork to a different format like TIFF.