I looked on their website and found that the quaker state advanced durability 30w oil is API Sn certified, but I've also read that Sn will work with older vehicles, is this true? Next time I get the chance I'm going to put some of the valvoline VR1 straight 30W in there, better safe than sorry!
Just a suggestion, but even though you don't drive in the cold, I believe a multi-weight 10w-30 or 15w40 would serve you better. Faster circulation on initial start-up, easier to pump and less windage friction. I think 20w-50 is just too heavy, but I'm biased due to my racing mind-set. Higher zinc content oil is still a good idea.
The new oil may "work with older vehicles", but with drawbacks. The 10% alcohol in unleaded gas "works in older vehicles" but reduces fuel mileage and doesn't like rubber. I'm sure that's what swelled up the rubber line in my few year old generator and started a leak. (This can get political, but I won't go there.) The newer oils likely don't protect as well. Remember, many cars now, particularly performance cars, have roller lifters, not flat tappets.