These work decently. Not as good as an official xbox one power supply though by any means. Also note that this adapter will not work with a xbox 360 slim power supply. It will break the console.
@poop it says on the amazon page towards the bottom that it does not convert from the 360 slim Psu so it does not work with the slim Psu. Either I'm high as fuck or Philly does not know what he is talking about.
Edit: http://www.amazon.com/gp/product/B00IG154KG/ref=ox_ya_os_product_refresh_T1 look towards the bottom