By Lucia Mutikani WASHINGTON (Reuters) – U.S. consumer prices unexpectedly rose in August and underlying inflation accelerated amid rising costs for rents and healthcare, giving the Federal Reserve ammunition to deliver a third 75 basis points interest rate hike next Wednesday. The surprisingly firm inflation readings reported by the Labor Department on Tuesday were despite an easing in global supply chains, which had contributed to a surge in prices earlier in the year. With a resilient labor market supporting strong wage growth, inflation has probably not peaked, keeping the Fed on an aggres…