Just to provide a bit more context to this, when it comes to a fan header an easier way to look at this is in amperage. Most fan headers can provide 1A safely. Most case fans are around 0.15A-0.25A however some are not and its important to look at the tech specs of the fan before splitting to 3.
For example the Corsair AF120 fan is only 0.18A, so running 3 on a header is no problem. However the Corsair SP120 (which generally you would use on a radiator anyway but the point still stands) pulls down 0.40A, so 3 on a 1A header is a nono. As a rule I try to avoid more than 2 fans on a single header for this reason.
Coolermaster lists that fan current at 0.16A:
https://www.coolermaster.com/catalog/coolers/case-fan/masterfan-sf120r-rgb/
However they note a "fan safety current" of 0.37A. What that tells me, is they believe it can surge to 0.37A for whatever reason likely when ramping up. So to me, I would never run more than TWO of these on a single fan header.
RGB runs off a separate wire and header, 15w should be plenty for 3, they pull down 2w tops each fan, I don't know where he got the 5w number, the RGB is rated at 0.4A at 5v.