TDP vs PSU power?

[kaitanium]

Looking to build a lower power system and was wondering if gpu tdp is like 140watt, why do they recommend a minimum 500watt psu? going for a 65watt i5 (haswell) also.

 

[millwright]

Because there is a CPU, motherboard, Hard drive, Memory, CD ROM, and they all need power.

A 500watt requirement, is because of crappy power supplies. the real requirement is about 450 watts, if you get a quality brand.

 

[k1114]

The psu will be higher than your actual usage. This is so you are not overworking the psu which will kill it prematurely. Also the best efficiency is ~50% capacity so you want to stick around there with peak at ~70%.