what happens if power supply is insufficient?

Depends on what model it's rebranded from. Most of their low- to mid-range units are rebranded CWT or GreatWall. High-end to premium units are Seasonic or Flextronics. CWT is a "get what you pay for" manufacturer, so generally the more pricier units are more reliable.

yeah I meant their higher end PSU's like my current RM850x
The RM850x is CWT. Same as my old HX850. It was a good unit.

the very top end PSU's don't seem to offer that much more value for the price for the average consumer...I always go for Corsair PSU's which get the best reviews in terms of performance and reliability...that's like buying a 3090 Ti or Titan every time versus the tier below...yes they will technically be better performing but not worth the price premium (for most people)