Well, it's *possible* to get two bad power supplies in a row. Not likely, but possible.
More likely, it's either a power-switch problem, or a mobo problem.
If it's a switch problem, replace it and you're done. (this just recently happened to me)
As you know, most modern machines have a power switch that connects to the mobo, where the power is controlled. Remove the power cord from the back of the PC, Remove the power-supply connector on the mobo, remove the power switch connector on the mobo, clean the connectors revealed in above. Use contact cleaner, if you have it, reconnect everything and try again.
In my experience, 90% of electronic problems are crappy connections.
If the above doesn't work, most likely you've got a fried mobo.
Just my thoughts. Folks here may have a bunch of other ideas.
Good luck.