that card recommendation has 300w psu...i am using it currently with a 450w psu, as u can see in my signature...but 400w is pretty tight for overclocking...if u plan to OC then get a 450w or 500w atleast...
OC as in when u enhance the base clock to a boost clock rate...
http://www.tomshardware.com/reviews/geforce-gtx-750-ti-review,3750-15.html