Cpu will handle 1660s fine, it'll be a really nice step up from the 280x.
PSU on other hand is iffy, quality is questionable and more specifically age. These things just not entirely sure how it'll go. It's lasted this long and probably be fine with the 1660s consuming less power, BUT, if it was me id replace it on age alone. Anti ripple mechanisms in the psu do degrade over time potentially causing power spikes escaping to the components.
thank you so much finally a good response that i can work with . the money is no problem i just want the best graphics card for my pc without too much bottleneck . so the best one would be the 1660 super? and for the psu it is k its called "azza dynamo 850w power supply" it's been running well since 2012
thank you so much i will do that . ima get the 1660 super and replace my power supply ! thank you so much for your help boju i really appreciate it . you the only one i seen that gave a straight answer
Just on another note, if/when you replace psu, remember that any modular cables, cables plugged into the power supply must all be replaced. Not sure if your psu is modular or not/semi modular, but as cable reference, modular psu's can have plug-able (cables not attached to the unit itself) ATX 24pin, CPU 12v (4 or 8pin), Sata (Data cables are fine). Any power related cable connecting from psu to motherboard/drives and also graphics card's PCIe, replace with supplied cables.
Reason being is pinouts aren't unified across brands so positive/negative pins can be in different spots and using existing cables already layed out in the case and swapping psu over for convenience will be a costly mistake.