GPU =
75W (https://www.nvidia.com/en-us/geforce/products/10series/geforce-gtx-1050/)
CPU =
54W (https://ark.intel.com/products/88179/Intel-Pentium-Processor-G4400-3M-Cache-3_30-GHz)
Rest of your System (MB, RAM, HDD, Fans) = Definitely
less than 100W (http://www.buildcomputers.net/power-consumption-of-pc-components.html)
THEORETICAL TOTAL =
229W (with headroom already, but actual use, it's more than likely just
around ~150W at peak)
Assuming the above ~150W is your average draw, then, a PSU capable of outputting 300W is sufficient (50% of rated draw is the point where highest efficiency is obtained).
Getting a 400W-450W would allow you to upgrade to more powerful components in the future (such as an i7 + GTX 1060-6GB).
Whichever aforementioned PSU wattage you select, it is highly recommend to get a good quality PSU for longevity and reliability. I would suggest looking at the
Corsair CX450M:
PCPartPicker part list /
Price breakdown by merchant
Power Supply: Corsair - CXM 450W 80+ Bronze Certified Semi-Modular ATX Power Supply ($26.99 @ Newegg)
Total: $26.99
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-08-19 14:30 EDT-0400