I have a Corsair HX series HX750 750w power supply, and i would like to buy longer power cabels(from wall to PSU). Is there any thing I should keep in mind, other than the obvious things on the end, when buying a longer cable? The cable looks like the same one from my monitors but it is thicker. I am also looking to do this with my my monitor power cables.
The length of the cable will increase its internal resistance. Though, for the power involved with a PC, I doubt it is going to matter that much, as the cable is quite short. If you are planning on running the cable more than say, 20 feet, you should probably look at a better solution, such as moving the PC or having another power outlet installed.
If you use 125VAC as in the US, that comes out to a nice even 6 Amps of power being pulled from the wall, before PSU efficiency is taken into account. This is a highly variable topic, so I am not going to supply the information here, as I do not know how heavily you are loading your PSU; you can potentially draw more power from the wall than the 750 watts your PSU is rated at. This all depends upon its efficiency rating.
From a quick Amazon search, it seems that the price difference from a 14 gauge to an 18 gauge power cable is only a few dollars.
For clarity, a 14ga cable should be rated for around 15 amps at 125VAC.
If you have a kill a watt or other means of measuring your PCs power draw under full load, this should give you a good idea of what you should buy.
Remember Amps = watts ÷ volts.
General advice: Only buy cables that are certified with the necessary stuff and make sure they are within spec or better
Some specs to look out for:
Current rating: 15A (or >6 A in the EU)
Voltage rating: 120V (or 230V in the EU)
Insulation temperature ratin: 125°C or greater