thank you verymuch for your attention.
sorry i can't speeking well.
good power supply mean resist with noise, that in this forum ever discuss.
if only use 7805 (cheap one) my experiment (AT89C51 system) is not resist with noise. If I drive the relay and the relay contact connected with AC motor, sometime my experiment can't work properly.
I already try your answer solution.
Is the switching power supply is good one (TL497)?

thank you verymuch.

ivan