This is only possible with some special models of Power Supplies (PSUs) that allow digital monitoring - some manufacturers that make such PSUs are Thermaltake, Enermax, Corsair.
i don't mean directly total power...i have thinked something of more easy, like...i can see "gpu power" watt and i can see "cpu package power", now i do gpu+cpu to know my total, so isn't possible make a simple addition?
Such a number would be misleading, because it would not cover several other components in the system.
Also some powers reported can be only partial, i.e. GPU Power might cover only power consumed by the GPU chip, or only its core rail, or can be only an estimation of power (not truly measured).