As the power supply was included inside the monitor, there wasn't an external power supply either.
If you bought an Amstrad CPC together with one of the green screen monitors [[Amstrad GT64/GT65 Green Monitor]]s however, you might have wanted the ability to play games on the colour TV-set later, so Amstrad also made the MP-1/MP-2 devices.
They provided the power needed by the CPCs, so that you didn't have to carry the monitor around just to have power, and a TV-modulator which modulated the monitor signal in a way that it could be seen on a regular TV-set.