How to avoid getting paint into sockets when handpainting.

If it were me I would take the switch plates off, paint, and when dry, replace. Or take painters tape and place it over the plug.

Take your switch plates off, and cut your electricity off first, then undo your sockets, put a small piece of tin foil in the little holes, then you can either paint them with a brush, sponge brush or spray paint them. Don't stick tin foil in the holes if they're still attached to the electrical wires. Take the foil out after dried and put them both back on the wall. I've seen painters paint over the whole plate and socket. I spent days scraping the paint off the socket.

Agree with Naomie that for your money and time, it would be easier and more cost effective to just unscrew them and replace with brand new.

Have you looked on eBay? There are thousands of replacement light switch and outlet covers available at many different price points.

take them off the wall (just a tiny screw holds them on usually) put some painters tape around the sockets and switch if you are painting the walls.

Tame the switch plates off before painting.

You can fold painters tape and slide it in there, too, I did that with doorknobs so paint wouldn't get into the key lock mechanisms.

You can also "dry brush" the outlets -- just a tiny bit of paint dabbed or stippled on carefully so it does't drip into the little spaces.

You just need to remove the wires attached to the receptacle before putting the tin foil in there you can put a piece of cotton or crumpled paper, piece of fabric, just so the paint doesn't get into the little holes.

Then after it's dry you reattach the wires to the box.