how many watts for OC

Solution
A good 550W PSU should be more than enough for that rig considering OC and future upgrade to more powerful GPU. Recommended PSUs: EVGA SuperNova G2 550, Corsair RM550x, Seasonic G-550.
You can do better for the money.

PCPartPicker part list / Price breakdown by merchant

CPU: AMD - Ryzen 5 1600 3.2GHz 6-Core Processor ($199.99 @ SuperBiiz)
Motherboard: ASRock - Fatal1ty AB350 Gaming K4 ATX AM4 Motherboard ($98.98 @ Newegg)
Memory: G.Skill - Ripjaws V Series 16GB (2 x 8GB) DDR4-3000 Memory ($119.89 @ OutletPC)
Storage: Crucial - MX300 275GB M.2-2280 Solid State Drive ($97.88 @ OutletPC)
Storage: Seagate - Barracuda 2TB 3.5" 7200RPM Internal Hard Drive ($66.89 @ OutletPC)
Video Card: Zotac - GeForce GTX 1050 Ti 4GB OC Edition Video Card ($145.18 @ Amazon)
Case: NZXT - S340 (White) ATX Mid Tower Case ($69.99 @ Amazon)
Power Supply: Corsair - CXM 550W 80+ Bronze Certified Semi-Modular ATX Power Supply ($37.99 @ Newegg)
Wireless Network Adapter: Gigabyte - GC-WB867D-I REV 4.2 PCI-Express x1 802.11a/b/g/n/ac Wi-Fi Adapter ($29.99 @ SuperBiiz)
Monitor: AOC - G2460VQ6 24.0" 1920x1080 75Hz Monitor ($169.99 @ B&H)
Mouse: Corsair - Sabre RGB Wired Optical Mouse ($40.00 @ Amazon)
Other: HyperX Cloud 2 (Gun Metal) (Purchased For $99.99)
Other: Windows 10 Home (Purchased For $26.00)
Total: $1202.76
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-07-04 02:23 EDT-0400