You need to provide the system model information.  On some systems, the power supply can be upgraded.  On a good number of others (particularly the very small chassis systems), it cannot.

I’m not sure what you mean, I just got into the pc making hobby. But to start off with, I got a Optiplex 3020 Tower with a base spec of i3 4130 (3.4ghz), 6gb ram ddr3, and a 800gb hdd. This PC has a PSU of 290w, and I assume I need to get a better one. I plan on keeping most of the parts, except for adding 1x4gb ddr3 to make it 10gb (1333mhz), adding a 500 gb ssd, and finally a GTX 750 ti. Now I plan on moderately overclocking cpu & gpu when needed, so I am unsure if I need a more powerful PSU. I also don’t know what type of cables I need for monitor, power to pc, or gpu.