WASHINGTON, Jan 13 (Reuters) - President Donald Trump has signed an amended version of an executive order that bans U.S. investments in alleged Chinese military companies, the White House said on Wednesday. The changes strengthen the initial order by requiring Americans to completely divest their holdings of securities of the blacklisted companies effective Nov. 11, 2021. In the initial version of the order released last November, U.S. investors were only restricted from buying those securities by that date. Reuters had previously reported that the change was under consideration.