As above, 3 PSI. The most common aftermarket electric pump will be the cube shaped Facet pump. They have several different pressure ranges available. The one rated for around 3-4 PSI is what you want. Any higher pressure than that will start to overpower the carb's float valve.
You asked for a link. See eBay item number: 271057209607
I am not endorsing that auction or vendor. You can probably get a better price shopping around. The information above is provided only to give you an idea what you are looking for.
There are also the Facet "top" pumps (Gold Top, Silver Top, etc). Those are cylindrical body pumps with domed ends. They are larger and more sophisticated. They are nice pumps but they cost more than the cube pumps.