but your risking everything else in the case.. to save £10 or so....
if it goes and your not lucky next time, then you could lose all the data on your HDD (precious photos and things) all your hardware, trip out the circuit in the house, cause a fire (possibly), require you to buy all new kit... or the whole shabang.. and with the cheap PSU you are losing money in the mean time as it has lower efficiency...
so the £10 that you have saved now could turn into £400+ in the future........