1) You can use websites like pcpartpicker.com to check the estimated wattage. According to that site your PC will draw less than 300W. I think you may want to buy the PSU that depends on the wattage. If yes, you will need a good brand at least 400 or 450W PSU, if want more headroom, 500W should be more than enough, like SeaSonic M12II 520 Bronze EVO for $35 after MIR
https://www.newegg.com/Product/Product.aspx?Item=N82E16817151093&ignorebbr=1 Keep in mind don't buy the non-brand or low quality PSU.
2) If you want to know the exactly wattage, buy one Electricity Usage Monitor like in the linker: https://www.amazon.com/P3-P4400-Electricity-Usage-Monitor/dp/B00009MDBU/ref=asc_df_B00009MDBU/?tag=hyprod-20&linkCode=df0&hvadid=167125429392&hvpos=1o1&hvnetw=g&hvrand=3256511119059383222&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9004526&hvtargid=pla-306572288073&psc=1