Patuoxun via Amazon offers the Mpow 30-watt 4-Port Portable USB Charger in Black or White for $19.99. Coupon code "U30WMPOW" cuts it to $13.99. Plus, Prime members bag free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, it adds $6.98.) That's $3 under the lowest total price we could find for a similar charger. It features flip-down AC prongs and over-heating protection.