On Saturday, February 17, 2018 at 2:22:46 PM UTC-5, Davej wrote:
On Wednesday, February 14, 2018 at 11:23:37 AM UTC-6, Pat L wrote:
I bought two mahjong machines in China to use in the US but I forgot
they use 220 over there. So I want to install a US 220V 20A female
receptor by using two legs of 110V 15A circuits and mounting a box
next to one of my 110v outlets.


No. Have an electrician run a new 240VAC line from your circuit
breaker box to an appropriate outlet. Of course USA power is 240V
60Hz rather than Chinese 220V 50Hz so you will need to check the
power specifications on your machine. An auto-transformer could be
used to reduce the voltage. You cannot safely connect out-of-phase
outlet circuits to be used together as you propose because of the
resulting short-circuit behavior.

Which is ridiculous because there is no short circuiting behavior. The op could do what they proposed and get 240v from two circuits on different legs. It would work, but I don't see a code compliant way.