The 661rpm is too slow according to the 1,400-3,200rpm range seen in the vendor's information there. You may have a bad fan on it where it is binding up. When was it put on? Just lately the fan on an aftermarket HSF quit suddenly after having been running to quiet for a period of time. When it was first installed you could hear a rattle when it speeded up during gaming or running a large app. The 50C seen if at idle is definitely high due to the fan on the sink itself running too slow to begin with. That will climb right up if you start pounding on system resources with a large program even gaming.
The 28,761rpm seen on the other fan sounds like the fan itself is drawing too much current even though psu fans work hard to cool the supply down when a large amount of power is pulled from it. You should look at the specifications for the supply itself at a vendor or manufacturer's site to see what the normal speed range is. Meanwhile you may want to plan on getting an alternate HSF setup if the temps there go much higher when you are at idle. A good aftermarket cooler should be seeing better then the stock temps while 50C is still within the normal range. A look in the bios at the hardware monitor if the board has that feature may give you a better idea of the actual temps. Sometimes the software monitors can be way off meybe even showing less then the actual.
