colourless fumes/smoke, the PSU? Please help.

periodically, and more often than not at the end of of a system boot my PC churns out what seems to be an endless supply of colourless fumes/smoke. I can definately smell and feel it as the air is generally thicker.

I'm convinvced it's the Power Supply Unit at fault, but not knowing an awful lot about PCs I'd prefer not to splash out on a new one and find out how wrong I was, so I guess I'll turn to you lot

I am using an MSI board and running the PCAlert program I occasionally get a warning about my voltages. It's usually the one 12+, marked red and below that number.
current numbers are: 1.74 (VCore), 3.09 (3.3v), 4.81 (+5), 11.82 (+12). Now I'll admit I have no idea whether that's good, bad or normal but as the PSU is a leftover from a previous machine I'm inclined to believe it's the culprit.

CPU temps are around 40-50, 30-47 for the System.

Am I right in thinking that this could be the PSU's fault, and if so is there any risk of damage to other components, or anything else I should be worried about.
In particular my WesternDigital 80GB HardDisk which tends to make a whining sound/revving sound now and then (previous WDs didn't produce this noise).

I'm looking into getting an Enermax PSU to replace the current one which is a mercury 300W (20a, 30a, 10a listed on the side if that means anything)
Any recommendations as I'll be hoping to get one cheap and so want to avoid making the mistake of getting a low quality version.

I'm thankful for any help you can give

While PCAlert shows only the +3.3V line being too low, the accuracy of such programs cannot be trusted because the voltage sensing hardware built into motherboards isn't very accurate itself. But Mercury is a brand from Deer, a company with one of the poorest reputations in the power supply business, and I would not want to risk my computer or data to any of their products. Also if your MSI motherboard has a 4-pin square power plug in addition to the 20-pin plug, it may be consuming over 8A from the +12V line, meaning the Mercury's 10A rated capacity for this voltage will leave little capacity to run the motors of the hard, CD, and DVD drives. Replacement with an Enermax, Antec, Fortron, or Sparkle would certainly be worth considering.

My system specifications are: 1700xp, 512Mb, GF4ti4200 & 2 case fans with an MSI KT400.
I plan on upgrading the graphics card with either one of the latest FXs from Nvidia or an ATI, and I use USB Keyboard/mouse/modem.

an estimation would be great thanks

trouble is I don't live in the U.S and newegg don't ship internationally, nor can I find a fortron online anywhere else.

I have found some Enermax models and here, in order of wattage are the names and prices.

-350W Enermax EG365AX-G-FMA II PSU with Manual Fan Control/Temp Control 2Yr (£39)

-433W Enermax EG465AXVE-W-FCA PSU with Manual Fan Control/Temp Control 2Yr (£92)

-465W Enermax EG465AX-G-FMA II PSU with Manual Fan Control/Temp Control 2Yr (£59)

Why is the higher wattage Enermax cheaper, what's the catch? £90 is a bit steep, so i hate to be a pain but on the basis of what I've said previously what would you all recommend?

Take atleast the 350W Enermax and you should be alright.

I love my Delta 60HP 7000 RPM fan that puts out more dB then CFM