First my Specs:
Ryzen 5 1600 OC at 3.750ghz 1.27500v
Red Devil RX 570
FSP Raider 650W 80+ Silver
AsRock AB350M Pro 4
Corsair Vengeance LPX 2x8GB 2400mhz
SX8200 Pro NVME 512GB
Seagate Barracuda 1TB
Seagate Barracuda 320GB
Storm Scout 2 Case with 6 x 120mm fans.
NH-D15 Cooler

Location: Philippines

Hey guys, I've been experiencing fairly random restarts on my system. It always happens whenever I play games or anything that stresses the GPU. I suspected my GPU at first; an R9 380, then I replaced that with an RX 570 but I still get the reboot issues. Same trigger and randomness. So I suspected my PSU next, it's 4-6 years old by now, an FSP Raider 650W 80+ Silver. I'm looking at the Corsair CX550M(gray sticker) to replace it with and fits with my budget of around Php.4000/USD80. But then I started suspecting how common households in the rural parts of my country experience power fluctuations of varying degrees. I can tell from how sometimes the room fan spins faster or slower even if it's set to speed 1. That leads me to thinking maybe I just need an AVR. Just want to ask if you guys can help me pinpoint which is the likely culprit?

If it's the PSU, while the CXm series are generally well regarded, are there other PSUs in the same price range that might be better or less expensive but has the same quality? The store link above is where I'll most likely buy it from and they offer other PSUs.

If it's not the PSU and I need and AVR (or UPS with AVR) how do I choose a good one?

Thanks guys.