Pictured on the right is my current collection of plugs and chargers - North American-type plug for (locked) Canadian cell phone, UK type plug for UK phone, charger with Europlug for South African phone (not ideal, but the phone was only $15), plus a UK and South African adaptor thrown in for artistic effect.The theory of optimal currency areas should apply to electric current and plugs, too. Multiple plug types, like multiple currencies, impose costs on travellers, and are a barrier to trade. This argues for widespread plug standardization. So why does it face resistance? Is there a potential difference between currents and currency?