I have a Mac Air 13" and an iPhone 5. Is there a power cord / adapter that will work for both of them? My goal is to be able to plug one power cord into both of them.
No - there isn't. MagSafe is a 5 pin (mirrored - so really three total pins) for high current and wattage charging. The other is a 16 pin, much more adaptable digital interface that can embed USB as well as carry data and charging and audio signals.
Newer USB-C Charging MacBooks will charge over the same sort of USB power delivery that Lightning is supporting - to the future you wish will be here as soon as you step away from MagSafe based hardware.
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