Tensun via Amazon offers its Tensun International Travel Plug Adapter with 4 USB Charging Ports in Blue, model no. 6576461, for $17.99. Coupon code "TENSUN34" cuts the price to $11.87. Plus, Prime members receive free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, shipping costs $6.23.) That's $27 off list and the lowest total price we could find. It features four built-in plug standards (US/EU/AU/UK), four USB charging ports (two with smart charging), and a slide-out plug release button.