You could have very well literally burned the PSU block out. Safety fetaure would mean you blew the fuse in it. Either way, I doubt the power block is user serviceable. You'll probably have to get a replacement.

Even if the thing still works (somehow) after you let it cool, it might have a shorter lifespan now.

GPU's can suck up a significantly higher level of power than any CPU I know of. (CPU don't go past 130 watts in most cases. Video cards can hit 300 watts with dual GPUs, 225 watts single GPU. At least in desktop. Laptop GPUs tend to be lower power versions unless you're talking gamer set-up. Laptop CPU usually don't exceed 65 watts; 35/45 is more typical.) An overclock (with or without overvolting) doesn't help matters. You might've been pushing the PSU at max or higher capacity for far too long. The biggest power blocks I've come across are only rated at couple hundred watts max.

I'd get a new one and tone down the settings just to be safe. Unlike desktop systems, you generally can't get a power block rate with lots of headroom. (Manufacturers tend to be very good at matching PSUs to needs, if not slightly undermatching them in some cases.)