Lurico via Amazon offers its Lurico Dual USB Charging Port Universal Travel Adapter Power Plug for $11.99. Coupon code "PNO8MKGM" cuts that to $7.99. Plus, Prime members bag free shipping. That's $12 off and the best price we could find, although we saw it for a buck less in April. It covers over 150 countries and features surge protection.
Note: This adapter does not convert voltage.