upsample2x doubles the rate at which the analog signal is sampled. Essentially, you get “inbetween” pixels representing the analog signal at the point between two pixels. It has the effect of softening the image, which can look good for some e.g. 3d games.
I think it’s disabled for all optimized modes however, so changing it probably does nothing when the PSP mode is enabled. If your screen doesn’t flicker when toggling it, it’s doing nothing.
And could messing with the sampling and lpf thing help me get the 480×272 mode working? I have no idea what either option does.
Unlikely. If my theory about your TV only supporting 203 offscreen lines is correct, then it won’t help. Having those set wrong however can make your image blurry, hence why I thought of it when you said the image was somewhat blurry. The correct values for that depend on console, cables, ambient RF noise in your room, etc., so I can’t say what yours should be… I can only say what I do for my setup.