That is an off brand OEM cheap power supply. It can only provide a sustained 268w under load and 18A, IF you assume it can actually put out it's rated power. It's DEFINITELY not a 500w unit, which would not be enough in any case for the GTX 970. I wouldn't use that power supply with ANY aftermarket graphics card that requires supplemental power through a PCIe 6 or 8 pin cable. In fact, that unit may not even HAVE a 6, 6+2 or 8 pin PCIe supplemental power cable.
If you want to upgrade your graphics card, you will need to upgrade the power supply as well. The GTX 960 would be a HUGE upgrade over the GT 620 and only needs a good 450w unit. What country are you in? I can recommend a good GPU and PSU upgrade based on what's available in...