What about the bit cheaper AMD RX 5700XT? A RX5700 is even cheaper so you could get a new power supply. That system does have a limit because it's still a Quad core cpu, so going above a certain card will no longer give you much more fps in gaming.
https://www.tomshardware.com/reviews/amd-radeon-rx_5700-rx_5700_xt,6216-2.html
Zotac's RTX 2070 Super AMP Extreme is priced only $10 higher than the NVIDIA Founders Edition, yet offers a much better triple-slot, triple-fan cooler and also includes an overclock out of the box. During gaming, the card stays quiet, yet manages to beat Founders Edition temperatures at the same...
www.techpowerup.com
https://www.pcmag.com/compare/370011/nvidia-geforce-rtx-2060-super-vs-amd-radeon-rx-5700-which
The power supply has a single 6 pin PCIE connector. It's 25amps so times 12volts that's 300watts. So max is 250 watts. The APU you have is low wattage at 65watts. Then 20watts for the system. That leaves 165watts. It should work but the powersupply fan will rev to max trying to keep it cool. There is a chance that after a while the extra heat will cook the power supply or it will trip out after a long gaming session on overtemp protection.
That 165watts is split up between the 75watt pcie slot card draw, and any pcie connectors to it. This varies because some cards draw more power from the slot vs. pcie connectors and some are the other way around.
Most cards need 6 and 8 pin PCIE connectors. Some GTX1060's and 1660ti's or the 1660 should work with a 6 to 8 pin adapter. A few of them might be a 6 pin version. Some brands come with a adaptor. At 125watts these cards will be ok with that power supply.
My advice is a RX5700, New Power Supply, Budget boot SSD . A M2 slot NVMe ssd is the fastest, there are some 256gig ones out that are fairly cheap. A regular SATA ssd is still way faster than that 1TB HDD. Use the 1TB drive for your steam folder, ect.
Power supply link..
Available @ CCL: Corsair VS Series VS350 350W ATX Power Supply. No Certified, 4 x SATA, 1 x 6-Pin, 4 + 4-Pin CPU, 140mm Depth., Mfg Code: CP-9020095-UK
www.cclonline.com