These days, when people buy a powerful new computer system, weather based on athlon64 or Intel Pentium 4, or Celeron D or Sempron, weather they buy a 6600GT or 6800GT, they forget about the most important & vital component of the system, The SMPS. SMPS stand for Switch Mode Power Supply, one myth people have that with a high power SMPS, in wattage, they will get high electricity bill, but itâ€™s wrong, even if u have a 800W SMPS, if u use only 300W, then the rest of the 500W is simply working idle & wonâ€™t add up to the electricity bill. Usually people go with the SMPS bundled with the cabinets they choose, cos the price is included in it, now in many cases, this bundled SMPS is enough for the tasks, but in few cases itâ€™s not, because of which is advised to go for a discreet Power supply. Also with the ATX 2.03 specification, Intel & AMD require a 24-pin power supply, & PCI-E based cards also needs extra power To calculate how much power supply U need, I strongly recommend that you visit here,which can give u a pretty solid rough measurement of your power needs, for your components Now, U know your power needs, itâ€™s time to calculate how much actual wattage your SMPS will provide, the best way to do is to check it by an electrician, but u can calculate it on your own too All the SMPS, weather bundled or not, come with a power supply measurement label applied to them, basically itâ€™s like this +12v = xx A +3.3v = xx A +5v = xx A etc We use simply the equation Power (W) = Volt X Ampere Now calculate, it, & U will get the exact measurement about how much wattage your SMPS can actually provide. But, since there is always some loss due to heat, decrees 5% of the total wattage of the SMPS from the total wattage Suppose U have a 400W power supply, which gives about 350W power when calculated by the above formula, and then simply subtract 18W from it, as heat loss. This new value is the actual power of your SMPS Right now, in India, exotic power supply brands like Antec or Enemax are hard to find & if found they are costly, a lot costly. U can go for a few good alternatives, like VIP, Powersafe, and a fairly new-comer here these days Colorsit, I gave a Colorsit SMPS to a friend a few days, ago , the Model number is M-330U, which as calculated by the label gives 425W power, so itâ€™s about 410W approx. which is shockingly good. They also have a Silent Power 12 CM version which has a 12 cm, fan just above the CPU, blowing air outside, & indeed it is silent, the ceiling fan makes more noise. The other options are Standard Model & a Dual fan model, U can check them here For a thumb rule, I m providing an estimate calculated power for system having Celeron D & Sempron = 260W Athlon64 = 340W Pentium 4 LGA775 = 350W Keep in mind that with this system I m adding the other components power too, which included, I combo drive, 1 HD, 2 Ram modules, no monitor, 1 GFX card, (6600 level), 2 case fans, usage may very depending on various other components used.