The original 63w 5150 PSU is quite sufficient for the 5150's intended use as it came from the factory, My 5150 later model has original 63w PSU, 2 full height floppy drives and when i got it had a 20 Mb Plus Card in it, The PSU had no problems coping, My 5150 now has a VGA card and XT-IDE and has no problems.
It's when folk started fitting a great honking power hungry MFM drive that the 63w PSU struggled and a more powerful PSU was required, I don't own a Gotek but i very much doubt it will make any difference power wise and a 3.5" floppy won't.
These old PSU's are 30+ years old and will fail eventually, It does not mean they are garbage, How many PSU's manufactured today will still be alive in 30+ years time ?, From what i have seen very few if any at all.
As already noted a 130w Original XT PSU will drop in to a 5150, But buying used is a gamble as it may last 5 minutes or 5 years.