So if they spec the full thing at 320 watts. Take off about 20 watts for SB and your negative rail(it is actually 17.4 watts).
This leaves you with 300 watts for EVERYTHING else. You video card will take about 100 watts.(so most of that should be able to come from the board).
https://www.techpowerup.com/reviews/ASUS/GTX_950_STRIX_OC/28.html
The board is rated for cpus of 95 watts and less and I do not think the i5 2500 takes that unless under very heavy load.
This leaves you about 100 watts for the SSD/Optical/Board. Remember all your other devices will use the 12 volt rail as well. It must be converted to 5 volts as needed on the board. This is different than on normal systems that have a dedicated 5 volt rail(that comes off the 12 volt rail, but inside the power supply instead.). All these numbers are full load and very few systems reach such loads, but do also have very short spikes of very high load. This is where power supply quality comes into play since these spikes are very short, but can exceed the parts normal peek load for very short times.
So now it is upto you if you wish to try this or not. No one can promise it will work or burn down the house(should not to this unless it was a VERY bad power supply).
I am not disagreeing with others about a risk. based on past experience computers are more power friendly than some may think(and low quality power supplies have driven up the amount of power a user thinks they need.) and very few push them that hard(at low loads everything clocks down to save power). Highest my UPS shows(at the unit so after power supply losses) is about 341 watts for 2 computers(one gaming[2600k @ 4.4 and a gtx 1070 gaming and one i5 750 with a gtx 650ti idle] one idle and my monitor.)
I was using an old i5 750 + 5770 on a 300 watt power supply with 264 watts on its 12 volt rails without any issues, but my board is a pretty friendly mITX board and the cpu is quite friendly as well(even with the 95 watt rating that all the cpus of that family share)
If you can get a power use meter from a hardware store(If you have a UPS it may also list power use in its software) you may be able to get an idea of how much power your computer uses. These at the wall readings tend to be higher because of power supply losses. They are not fast enough to see these spikes, but will give you a decent idea.
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