I struggled with the Sunlu 250g spools and tried a few different spool holders. I found the 'AMS Lite Small Spool Securing Cap' by dandcmckay and it worked but the spool was extremely loose and I got a few tangles. I created the 'Cylinder_250g_Spool' adapter initially but updated it with this easier 'screw-on' feature. It fits the bare spindle of the AMS Lite and fits inside the 250g spool but not tight. My model printed in 2 colors as I ran out of the filament on the spool and finished it in yellow.  :-)

It is 2 parts, takes about 30g of filament to print and has a screw on nut. This makes assembly easy.

Steps:
1. Put the 2 pieces together on either side of the SUNLU 250 gram spool and screw them together.
2. Remove the AMS Lite Rotary Spool Holder from position 2 or 4. This is done by simply pulling it off. (You pushed it on when assembling it when you first assembled the AMS Lite. It goes back easily when done. 
3. Slide the Spool adapter with the filament onto the spool.

Optional but suggested..
4. Secure the spool and adapter on the spindle with the 'AMS Lite Small Spool Securing Cap' by dandcmckay.

NOTE: The 'AMS Lite Small Spool Securing Cap' by dandcmckay ONLY works on position 2 and 4 on the AMS Lite. These are the YELLOW colored spindles. See his post in Makerworld for details and STL files.

Thanks to dandcmckay for their 'Cap' and the spool does not fall off the spindle anymore.