What are the lightest travel adapters/converters available for France?

Get a European USB Charger

I would buy a USB charger with a European plug (image courtesy of aliexpress):

^{Travel Convenient EU Plug Wall USB Charger Adapter For Samsung Galaxy S5 S4 S3 Note 3 by Ali Express, fair use}

It beats the weight of your US charger plus a plug adapter, it's cheap a as dirt (2-something bucks on eBay), it can be used for all your USB-powered devices, it comes in single- and multi-port, and will work in most of mainland Europe. Indeed it will fit in the European CEE7 standard plugs, the Italian standard plugs and the Swiss standards plugs. It will also work in other countries using similar 2/3-holes plugs including, and not limited to, Argentina, Uruguay and Brazil.

If you can't secure one before flying to France you'll be able to find them in any electronics brick-and-mortar shop at a street retail price I.e. more expensive (say FNAC for example), or in one of those generic shops selling made-in-China products.

Or a Plug Adaptor (and maybe even a Converter)

If you want to use your US-plug USB charger, you'll need a US to Europe plug adaptor (or a multi-country adaptor). You'll also need to check if your existing US device can take 220-240V/50Hz. If not you'll have to purchase a converter to lower the voltage and increase the frequency to 110V/60Hz. The converter is necessary to avoid damaging the charger, the device or yourself. For more information here's an interesting read on the topic.

(iPhone user here)

(personal experience) I use my usb adapter directly plugged in to the wall to charge my iPhone in Europe (France, Italy and Spain)

The Samsung S3 charger should directly support 110v/220v, you only need a plug adapter which is really small and really cheap.

Most electronics these days adjusts automatically for voltage. The charger for my iPhone does, as do all my computers. In that case all you need is a physical plug adapter like this small and light one. I have half a dozen

Try to head to Montparnasse rail station; the Relay stores often have them, due to the large foot passage of foreign travelers (though Montparnasse serves less destinations with different plugs as compared to Gare du Nord or Gare de Lyon). Another TA poster recently had luck at one of the Relay stores in Gare du Nord.

and i thought this adaptor is gonna be best with multi usb port and the multi socket ports you can charge your cell phone, tab, etc

I would suggest the Walkabout Universal Adapter with USB .It is a high probability that all your electronics are dual voltage.Walkabout Universal Adapter features a clever design which contains all the major adapters on the planet as well as two high powered USB charging ports. Input power: 100~250V. USB Max. Output power: 5V DC ~ 1000mA. AC Max. Power: AC 125V~6A / AC 250V~3A. CE and ROHS approved for safety.

1.With the Walkabout Universal Adapter, you eliminate the need of bringing any other chargers for devices that charge with a USB port. Cell Phones, PDA, MP3/MP4 players, iPod, iPhone, iPad, travel speakers. Supports higher powered items like iPhone 4/4S, iPhone 5 and iPad 4.

2.Even better, it has two USB power ports.

3.For AC Charging, use the plug for dual voltage laptops, netbooks, C-PAP machines. With a 100-250 volt output, you can use it anywhere on the planet Earth.

4.Can simultaneously charge devices through the USB and AC power sockets.

5.Has surge protection with safety shutout. Fuse protection as well.

6.Compact size, lightweight. Made of fire resistance materials

My suggestion is to take a multi-prise of your current country, open it up and change the plug to a European (that you should be able to find in stores in Toronto, or in the worst case buy one in Paris). The new plug should look like this:

Ungrouned, and a three-pin for grounded. Both use the same voltage, so there should be no problem in that region.

I would suggest The Walkabout Solution adapter. automatically adjusts incoming voltage, whether if you are in a 110-120V country (Like North America) or 220-240V country. (Everywhere else.) Output voltage is always correct for North American products. Even better, the built-in USB port also charges cell phones and iPads, so two items can be charged at once.