PSU issue?

[kully1972]

A friends PC doesn't power up unless you flick the PSU switch on/off repeatedly.
I can see the mobo lights turning on signalling power delivery but it won't boot unless it is forced as in the way described.
I've transposed the entire PC into a new case but problem still persists.
A new PSU has been ordered.(Seasonic prime 650w).
Present PSU is corsair AX750.
Is PSU tripping out?. I have encountered a similar issue afew generations back with the season xp760w which was solved by a new PSU.
Any advice much appreciated

 

[kully1972]

A quick and final update:
All resolved- machine boots up perfectly everytime with new seasonic prime 650w!
Must admit bitterly disappointed with Corsair AX750 that barely lasted 3 yrs.

 

[kully1972]

It was bought second hand on fleabay so I guess I shouldn't complain.
This prob voids the warranty but TBH my friend can afford to take the hit and it will get disposed of soon