The top element of the power switch broke in my daughter's Casio SA-78 keyboard, so I've designed a replacement part. It should fit quite tightly on the actual switch inside the keyboard. Source file for Fusion 360 included in case you need to tweak it

Print instructions:

I've printed it with PLA using 0.05mm layer (ultradetail profile from Prusa Slicer), supports and ironing enabled for nice top surface.