They've improved a bit over the years. The power screwup on the original Pi meant that some boards wouldn't work reliably at all with any power supply. (They mistook the 1.8v output from the USB+ethernet chip's internal regulator for an input and connected it to the 1.8v rail that powered everything else on the board, meaning that for some unlucky folks it ended up supplying 1.8v power to the entire board, overheating spectacularly, and falling over. It took an outside engineer to find that one after the folks who designed it blew off all the complaints about overheating Ethernet chips, USB falling over, etc as user error. In fact, they were so confident all the problems were user error that they banned the person who spotted their mistake from their forums for pointing it out.)

Can you list examples where it hasnt worked?

I support a USB system and I this was my worry since day 1.

Curious, and it would be helpful

Just get the official power supply then.