so ,I found this decent deal with an i5 7400 and 12gbs of ram . I wanna buy a zotac mini gtx 1070 for this upgrade. however I have heard that the default psu is only 300 watts,note that the zotac gtx 1070 requires a 500 watt psu . I know I have to replace the old psu, but I dunno which to choose since I don't have experience for building pcs. thanks guys.