there are 2 different soundbars one with pass through so doesn't require an external power supply and one without which does.
Dell AX510 Soundbar Speaker - for UltraSharp and other monitors with a power pass through connector
AX510PA Soundbar Speaker - for E-series, Consumer and other monitors without a power pass through connector (AC adapter included)
also there is this but im not sure what difference it will make
The AY511 Audio SoundBar with Virtual Surround from Dell ™ is designed to enhance the enjoyment of multimedia digital content. Its sleek design, and delivery of great sound perfectly complements the performance and style of the Dell ST, SX and UltraSharp monitors.
Compatible with SX2210T, SX2210, ST2410, ST2310, ST2210, ST2010 & ST2010-BLK and UltraSharp U2410 & U2711 monitors
i know this because i was toying with getting an sx2210 + soundbar