Don't know if this helps (or perhaps you already know about them) but in addition to our converters we bought these great multi device charging stations made by ZONE Electronics that roll up to the size of a cardboard paper towel roll for packing. I found them at CVS for $10 a piece just before our last trip to Europe and figured it wouldn't hurt to try. They are awesome! We bought them almost 2 years ago, have used them on every vacation since and they are still working great.
We've never been to Barcelona so I don't know how abundant the outlets are in their hotels, but in our tiny room in Paris and B&B in Rome they only had 1 outlet. Using our 2 charging stations (plugged in to our 2 converters) we were able to charge 3 iPods and 3 cell phones at once each night and then only had to charge our cameras batteries separately (only because our cameras are older and don't have a USB plug). They can each charge up to 4 devices at once (depending on what type of ports you have) and have a little baggie inside the storage compartment with adapters to match your device. On our Fantasy cruise we added a Kindle and iPad Mini to our charging needs and were still covered. If your local or other local drug store doesn't have them maybe
Amazon or eBay would or something similar for less than Sharper Image prices.