If you never intend to go higher than a 950 in terms of power, then a 400w PSU would work. That said, the one you linked, the N1 from Evga is not something I'd recommend. It's not the power rating but rather the quality of the part. Reviews of the PSU are, at best, not favorable.
If you want to go with a 400w unit, the cheapest I'd recommend is
https://pcpartpicker.com/product/HvTmP6/evga-power-supply-100w10430kr
or for a 500w unit
https://pcpartpicker.com/product/XCjG3C/evga-power-supply-100w10500kr
For a higher quality PSU I'd look at
https://pcpartpicker.com/product/4Vzv6h/seasonic-power-supply-s12ii430b
or
https://pcpartpicker.com/product/fZyFf7/seasonic-power-supply-s12ii520bronze
I'd recommend looking at the 500w units rather than the 430w units, so that later if you wanted to move to a Nvidia 1060, you'd enough of a ceiling so at to not run the unit harder than it has to.
For the video card you listed, I wouldn't bother buying used. New, with a rebate from Newegg, that card runs less than the used options on amazon.
$110 after rebate
http://www.newegg.com/Product/Product.aspx?Item=N82E16814487159&cm_re=02G-P4-2958-KR-_-14-487-159-_-Product
The 950 is a good lineup, but for a bit more you can pick up a R9 380, which out performs the 960 and a number of models run for under 200 after rebates. But I believe you'd need a 550w PSU for that. Something like this would work
https://pcpartpicker.com/product/2tckcf/xfx-power-supply-xfxts550w
or better yet
https://pcpartpicker.com/product/qYTrxr/evga-power-supply-220g20550y1 for a top end model. But at that point we may be going past where your budget allows.
As for the RX460, supposedly its coming out in a couple of days. I couldn't find a power rating for it so I don't know exactly how much draw it'll need. Judging from the pictures, it requires its own power plug from the PSU, so I highly doubt it'll work with the stock 200w PSU from Dell.