Faulty power supply or something else?

Not really. However, a modular (or semi-modular, as I have), can really help towards a neater build and can aid airflow (and therefore cooling) because there won't be any (or as many) unused cables to tie back out of the way.

As regards PSU wattage, a decent PSU rated at 850W is capable of providing that amount of power. Contrary to some beliefs, the PSU only draws the amount of power that is required by the load placed upon it (plus a small overhead consumed by the PSU itself).

A cheap PSU, such as one that comes bundled with a case, might be rated at 500W but in reality is only capable of sustaining much less than that. In addition, the overhead consumed by the PSU itself will tend to be greater.

The CX600 is a good choice too, I was only looking at the ones on sale.

I have 2 modular PSUs and I love them! One only has the cables needed.

Very good choice Losyak. If you do find a higher than 600W priced right buy it. No such thing as to much power. It's kind of like a care with 800 HP you can still drive around town with no problems. The horsepower is there but only used if and when needed. Their is a problem with modular power supplies. Once you use one your hooked. That is all you will ever use again.