Heat oil in pot over medium heat. Add ginger and garlic and cook for 1 minute. Stir in curry paste and curry powder; cook, stirring, until dark and aromatic, 2 minutes.
Stir in coconut milk, scraping bottom of pot; bring to a boil. Add chicken broth, fish sauce and sugar; bring to a boil. Reduce heat to medium-low and simmer, covered, for 10 minutes.
Add chicken; bring to a low boil. Reduce heat and simmer, covered, until chicken is cooked through, 20 to 25 minutes. Remove ginger and garlic; discard. Remove chicken and let cool for 5 minutes before shredding; return to pot.
Taste soup and adjust with more fish sauce or sugar, keeping in mind that the flavour will be diluted with the addition of noodles.
Meanwhile, boil egg noodles in large pot of boiling water for about 1 minute. Drain for 3 minutes without rinsing; divide among large, deep bowls. Top with soup, chicken, crispy egg noodles (if using) and a combination of shallot slices, lime wedges and cilantro. Serve with chili oil.