It is set to the resolution 1280x800, which is really handy for a 30" screen.
The usb2dvi adapter can only support a maximum of WUXGA in single link DVI mode, your 30 inch Dell LCD requires dual link dvi-d to work at its max resolution. If you use a single link dvi adapter your LCD only supports 1280 x 800 resolution.
Dell 30 inch LCD with WQXGA (2560 x 1600) combines two single link signal of 1280 x 800 into a 2560 x 1600 signal.
So in a nutshell, you can't use the Lenovo single link USB2DVI converter (recommended to support only up to WUXGA 1920 x 1200) to run a 30 inch WQXGA monitor or 27 inch 2560 x 1440 monitor at their native resolution.