Your power supply is not capable to provide proper voltage when you overclock, it is performing at it's maximum capacity before you overclock your video card.
I will do my best not to be technical here. When a component is not capable of providing the proper watts it heats up. When it heats up it is not able to pull the same watts as when operating within specifications. When that happens more wattage is necessary to produce the desired result.
The above is a dangerous scenario in part because it puts stress on components, including the PSU itself. This will lead to component failure sooner. In the mean time all sorts of odd things will begin to show themselves, such as odd behavior, Windows errors, slow downs, data loss due to damaged components due to fluctuating or lack of optimal amperage for your drive. I said I will try not to get technical, so, I will leave it at that, although there is much more.
Visit www.jonnyguru.com to get the best power supply reviews. Here a some power supplies that you can pick from, you do not have to purchase from them if you find a PSU less expensive elsewhere. Look to pay ~ 75 to 80 dollars U.S. for a good one. I do not suggest the Corsair VS series listed for $49.99
https://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100007657%2050001459%2050001697%20600479295%20600037997%20600037998%204814&IsNodeId=1&bop=And&Order=PRICE&PageSize=36
Personally I would lean toward the Seasonic FOCUS Plus for $79.99 if you use the promo code for a discount, it is fully modular, if that is what you want. Any of the listed PSUs between $70 and $80 will be fine for you. Modular, semi-modular or non-modular is up to you.
Also, I suggest you use MSI Afterburner to overclock your video card.