Super Smash Bros. Invitational @ E3 2014 participants+Details. NINTENDO Listened: GC Controller Adapter

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KingdomHeartsFan said:

Its also really weird that there's 2 USB ports leading into the Adaptor.

WiiU uses USB 2.0 only. So this is likely so the adapter can power up to four controllers. Had Nintendo spent a few cents and went with USB 3.0 then this wouldn't be an issue. (my assumption)