Most of the two-pin, European type, "Schuko" style sockets I saw along the way were in older hostals or albergues. They tended to be the two pin - ungrounded type - as opposed to the three pin grounded variety.
You can usually find a three-outlet, two-prong wall tap to share a single outlet with two others at any ferreteria (hardware store) or Oriental / China Bazaar shop in Spain. The first possibility along the
Camino Frances will likely be in Pamplona.
You can also these devices in St. Jean Pied de Port before you start. There is a Carrefour supermarket (Avenue du Jai Alai, on the north side, outside the town walls, down the street from the train station), and at least one magazin de bricolage (DIY store) "Philippe Garicoix," at Rue d'Uhar #6. I bought a three-way, two-prong tap here last year. It is through the gate, next to the church, across the bridge, first street on the right, then on the left.
Most small electronic chargers (Smart Phones, tablets, cameras, etc) come with two-pin chargers. The FIRST thing to check is whether the charger for your device is multi-voltage. That means, check the itsy-bitsy fine print that "folks of a certain age" (including me) must use a magnifying glass to see states: INPUT 100 - 240 VAC, 50 - 60 Hz. OR, it might state 110 - 250 VAC, 50 - 60 Hz, or something similar.
If your charger
DOES say this then you ONLY need the converter plug to change the shape of the pinson your charger to the two round-pin Schuko-type European plug. A two-pin EU plug / adapter will fit inside the recessed three-pin grounded socket.
If your charger
DOES NOT have this printed on it, then you will need to either: (a) obtain a European charger that works, and already has two-round prongs on it; or (b) bring along a power transformer that converts 220 VAC European current to 110-110 volt North American current. But bringing a second "thing" adds dead-weight.
Failure to do one of these if your charger is
NOT a multi-current charger will FRY your electronic gear. The plug shape adapter alone will not work unless the current capacity is compatible.
My personal solution was to buy an Apple iPad compatible charger in Europe. The ONLY difference between the North American and European chargers is the power prongs - and they are interchangeable. One thing I have NOT yet done is to find out if my local Apple store carries the two-prong European style head that will easily replace my two flat-blade North American power prong head. This would be the cheap way to fit me up.
I also bring a unique, multi-head charging cable I found on the internet. It plugs into a USB outlet (charger, computer, etc.) the multi-head has male plugs for my iPod Touch, micro-USB, and mini-USB devices. So, I bring one charger and one cable for all my devices.
I hope this helps.