Hello,

My girlfriend and I are super excited to be heading to France and Switzerland for two weeks in early August. We have secured a car rental in Lyon to head to Switzerland, circle back to France hit the Savoie, Northern Rhône and drop-off back in Lyon. I've read up a bit on the need for a Swiss driving vignette. I see it's 40 CHF. Is this sort of thing better purchased in advance online since we have some time. I imagine you can't get it from the French rental car dealership. I read that it is available in a few types of places once in Switzerland but am curious if it makes more sense to purchase in advance to save time.
Thanks for your help everyone!

First, you need to tell the car rental place that you are taking the car into Switzerland. Although I have not experienced your particular situation, in some cases rental places charge you and give you the vignette. Though I do not know if that applies in your case.

A lot of the rental cars in places like Lyon or Strasbourg already have a vignette on them purchased by previpus renters, so be sure to ask if they have any cars like that on hand. If not, you just buy thre vignette at the border crossing. If you don't take any Swiss autoroutes, you don't even need one -- for example, if you're only going to Geneva and are not on the autoroute. However, if you are driving around the country it is almost impossible not to need to take the autoroute.

As above.
You need a vignette if you enter Geneva on the motorway. That's "automatically" the case if you don't leave the French A40 motorway either at the exit of St-Julien-en-Genevois or at the exit of Archamps and reach the city center of Geneva from there on local roads.
Within Switzerland, you can always chose between motorway (with vignette) and cantonal road (through the the cities and may be the better choice if you want to visit the cities of Nyon (with castle), the Swiss National Museum at Prangins, the cities of Rolle and Morges (with castles), or the Lavaux vineyards and the cities of Vevey and Montreux).
You don't need a vignette either for the roads
from Montreux via Chillon castle - Bouveret Swiss Vapeur park/Aquapark - Evian (Fance) or
from Martigny via Chamonix (France) to Annecy.

As you didn't tell us in your previous thread what you really want to visit in Switzerland, we cannot give you more advice.

I once accidentally drove across the border on the A40 and told them I did not plan to use the autoroute. But the Swiss are very Swiss so I had to turn around and go back to the first French exit to get a normal road into Geneva.

.....that's why I mentioned the 2 exits of St-Julien and Archamps, both bien en France

more and more car rental companies apply an extra charge if you say you will cross a border. They claim it is for insurance but this is ludricous. I doubt that any company will provide you with a vignette. As said elsewhere, when you enter Switzerland via a motorway, you will be directed to the booth where you buy the vignette.

Ah so it's a pretty simple and straightforward process? I wouldn't really be saving much time or peace of mind by buying it in advance?

Switzerland not being in UE means that there are customs whenever you enter the country and it takes few minutes to buy the vignette there.
I am not sure that you can buy it outside Switzerland (they also sell e-vignette online but you need to provide the reg plate). It is different, let us say, for the Austria vignette. Since there are no customs between Germany and Austria, the german gas stations will sell the vignette.

Switzerland is fully part of the Schengen zone, so there are no systematic customs formalities. Most people just drive through without having to stop. There are spot checks from time to time. I was highly amused on the Lyria once when French customs frisked me at my seat, checking particularly to feel if I had any hidden packages around my waist.

I might be wrong but Schengen is about freedom of travel for persons, checked by police (border police, immigration,...) while EU is about goods, services - checked by customs - and persons (even if countries are allowed to be in EU and not in Schengen, like Ireland).
Obviously, customs checks are not systematic, even rare. I cant remember being checked in CDG or in US.
Coming back to Switzerland, the OP may however need to check the opening hours of the customs offices if he wants to buy the vignette when crossing the border.