so, why other sites ive ask recommend at least 450-750 watt?
Because they don't know what brand or model of power supply (PS) you buy. Thus the PS company's quality and veracity is unknown. If you buy a cheap PS from china, it might need to be labeled as 750W rated as compared to buying the "truepower" 350W version which would work the same. It may also have the 80% efficiency badge (which is probably fake). I only accept 80% badges from Antec, Corsair, XFX, Enermax/LEPA, or other major genuine manufacturer of their own PS. Do you remember those chinese-made speakers advertised as 450 watts peak power (but they sit on your desktop 7-inches tall)? How truthful is that watt rating? Another thing about PS is that the cheap ones that don't say "true power"(antec) or "full continuous power" usually mean the power rating is short-term peak power. For those supplies, the actual continuous power is 80% or less. In the "old" days of power supplies, I remember reading you needed to derate as much as 50% (wow!!!!) of the power rating for continuous 24/7 power. Thankfully those days are gone as 80% seems to be the norm for a major branded PS that doesn't have some sort of "true power" or "continuous RMS" power rating on it. If you see "continuous peak power" that is NOT "true power". It is deceptive wording.
In general, you can expect to be able to run continuously at 80% of the advertised power at room temperature if it is not a "true power" type.
*UPDATE* TL/DR
Even brand name power supplies can go bad on occasion since they either get parts or have the power supplies made by chinese fulfillment houses which do everything from designing, certification, production, badging, and packaging the power supply with the brand name logo.
Back in the 1990's and early 2000's, various mainland chinese (not taiwan who were above board) manufacturers would engage in scam operations. That included things like putting extra non-functional dummy parts on motherboards to make them more "impressive looking". They did that with consumer appliances too and even low-end transistor radios didn't escape with one model advertised as 9 transistor superhet but only 3 of the transistors worked. The other 6 bad transistors (reject failures) were in there to satisfy the advertised wording that 9 transistors were included. Other scams include use of regular electrolytic capacitors in smooth top cases to make it look like solid-state capacitors (tantalums). To keep from being sued by the FTC, a few of the capacitors would be actual solid state but the others were not.
Attitudes like that keep my corporation alert as we have to test and verify everything that comes in to make sure that we don't get baited and switched. That chinese attitude is also why I don't buy any frozen fish coming from China, especially the type that is farmed in the polluted waters (tilapia, dace, carp). As for intellectual property, the Chinese don't care. They will stamp UR, CE, FCC, or whatever certification logo on the device even though it doesn't meet qualification. I know they do this since a coworker inspected the insides of the same electronic item purchased a year apart. The insides were different and did not agree with the patent and picture information sent to the FCC and relevant certification office. This is why research & development can have a lot of hidden or extra costs just in rechecking and RE-certifying even test gear or assemblies going into a test rig or evaluation product. Was failure due to our design or chinese part failing after 100 hours of use? Also, our own certification processes are jeopardized when chinese-made sub-assemblies themselves have
falsified documentation or altered "bait and switch" manufacturing processes.
Anyways, getting back to power supplies, a more recent story from this past week of a PS having false ratings is at the URL below. Not only was the total RMS power inaccurate, the power factor correction did not exist even though it was claimed. Ha, ha. It's more of that "450W speaker in a 7 inch tall, 3 inch wide plastic case" nonsense.... Visit the URL and laugh at the fake parts inside the power supply including extra WEIGHTS to make it seem heavier because heavy power supplies from China must be better, right???? Ha, ha....
http://forums.hardwaresecrets.com/if-fake-wattages/7795?threadid=7795?goto=newpost-----
**bait and switch - I am misusing the term here because it is not the normal description of a salesman switching products on you at the retail store. In the case of manufacturing, the chinese supplier wants your business and for the first month or three, the items will be identical to the evaluation product, or the chemical purity will be accurate. But after a period of time, the chinese supplier will switch the product to something cheaper or take less care in manufacturing, or allow out-of-spec devices which still basically function to be shipped as fully-qualified in-spec items. That's because the chinese supplier assumes you have relaxed your guard after a few months have passed. People at my corporation have noticed this. Even the local fry's computer components manager acknowledged this with some of the items they get from china.
