Ah...Which Powder Brown do we speak of?? Ancanthurus Japonicus or Nigerians?
Japonicus is the hardier out of the two..And I would say survival rate is better than that of a Powder Blue..BUT..these are not easy fish.. They are prone to ich and other parasites [Velvet, flukes, copepods..etc..etc...] I have one, I battled ich with him..then some strange illness that made him all blotchy..At one point my fish was near death, lying on the bottom and breathing very heavy.. to this day am not exactly sure what was wrong but luckily the treatments I used worked..He is in my 240 and fat ,fat ,fat...He was clean of any spots when I placed him in there but now has little 'pimples' on him..No its not ich, [don't even go there

] It was brought on by the stress of moving to the new tank and being bullied.. It does not affect my other fish including my Hippo Tang..Whatever it is...there is no cure for it as this fish has been through it all!! My guess is a Myxospordean or Microspordean infection
I recently had a heater malfunction...my tank was up to 93

The only fish I lost was an Argi Angel...My Powder Brown survived..
So the point to my long boring post is...these are not for beginners or for people who want an 'easy ' fish..Do not get one unless you are committed to treating this fish in a quarantine because 90% of them will have some issue. Mine was in qt for 6 months. They are hardy once you get them past the ich and other problems , but it is a lot of work