Tronxy/Prusa top feed spool holder, Real easy and works.

thingiverse

This simply clips onto the top frame of your Prusa, any with a 7mm Perspex frame. And the spool sits atop. Simple and effortless. Print both the center rod and holder upright, with support and brim if necessary. I used 1mm walls and 70% fill for added strength. It holds full 1kg spools with ease. Use with 22mm spool centers. I've included the one I use as they suit most spools.