The retro-style smart speaker delivers powerful sound and offers simultaneous support for Amazon Alexa and Google a**istant. | Photo by Chris Welch / The VergeThere aren’t a lot of smart speakers on the market that support Amazon Alexa and Google a**istant simultaneously, which is one of the reasons the JBL Authentics 300 stands out. Unfortunately, it’s expensive at its full retail price of $449.99, but Amazon is selling the portable smart speaker right now at a new all-time low of $278 ($172 off).The midrange 300 can listen for wake words for both virtual a**istants and deliver powerful sound free of distortion at louder volumes, allowing it to outperform even the new Sonos Move 2. It also lets you play music over Bluetooth, Wi-Fi, or via an aux jack or USB-C, and it sports handy dials for easily adjusting the EQ. The speaker also looks cool thanks to a ‘70s-style vibe, which uses faux…