Foxin aren't even on the PSU tier list, so I'm not sure their power supplies are to be trusted. I would swap that out for a decent quality XFX 450W or similar. If you're looking at a new power supply, be sure to post it here first, as we can tell you if it will be good or not.
For a system using a single Radeon R7 250 graphics card AMD specifies a minimum of a 400 Watt or greater system power supply. The power supply should also have a maximum combined +12 Volt continuous current rating of 20 Amps or greater. (Minimum system power requirement based on a PC configured with an Intel Core i7 3.2GHz 130 Watt TDP processor.)
Total Power Supply Wattage is NOT the crucial factor in power supply selection!!!Sufficient Total Combined Continuous Power/Current Available on the +12V Rail(s) is the most critical factor.
Post a picture of the label on your Foxin SMPS if you want an accurate answer.
here this is my smps
http://postimg.org/image/45fuwh6m5/
That image is so blurry. Is it an FPS 500 or 600 or 800? The lack of a maximum combined +12V rating isn't encouraging.
Based on its +12V rails specs that SMPS should be capable of powering your system with a Radeon R7 250 assuming that the SMPS is actually able to deliver the power specified on its label.