So I have a power source outside to plug in some cafe/ restaurant style decorative string lights. Any ideas on putting a weatherproof wifi switch on it so I don't have to physically go out and plug it in?
You could do a smart outlet, or switch the recep with a smart switch. I don’t know of any that are weather resistant so you’d be out of technical compliance on that one. I have a Wemo switch outdoors in a box with a cover; doesn’t get directly rained on though. Would yours?
By the kitchen door (inside) I had 2 light switches. I changed the 2-gang box to a 3-gang. Ran a new feed to a new GFCI receptacle outside. I installed a timer in the extra spot... but I think a wifi switch could be substituted just the same.
Outdoors, you could try swapping to a 2-gang box and an in-use cover. Not sure how long a wifi switch will last in cold/damp conditions though...
I've been using this one for over a year now with some LED string lights on my back deck. No issues whatsoever and I have a schedule set up with Alexa where the lights turn on every day at 6:30pm and off at 11. It is under the framing of a fence but it is exposed to the elements and has held up fine.
FWIW, the Smart Phone/Alexa might be best for some applications, but wrong for others. I go to the hot tub at random times and wanted to walk out of the basement at any time of the evening, push a button and turn off the outdoor light over the garage. Home Depot had a unit with a small battery powered remote ON/OFF which I can leave by the door. No need to bring the phone or wake Alexa.
Plenty of options for outdoor wifi switch. I bought one for ~$25 off the shelf at Home Depot a few years ago and it's been turning on/off my landscape lights every day reliably. It can be exposed to the elements, but you'll want some sort of simple cover over it (underneath an awning, etc.) to keep direct rain off it or else it might pop your GFCI every time there's a major storm.