I do not think just yet, that its the power supply.
since you tell that it does it right in the middel of your work..
What does it do then.. Can you immediately switch back on, and is it an normal startup whit sounds and such??
could be the supply cable sitting loose, and it could be as easy as just being the power socket sitting crooked in the electrical socket...
but please bring som more info about what it can, and cannot do. and how often you have experienced this?