there is a tool that you can plug into the socket and will give out information on polarity and ground conditions. Its about $5. Its worth a check.
Secondly, an expensive $35 Surge protector is the key. They have a light on that shows its working and is protecting. You can even acquire one with insurance policy attached to protect your computer and periferials. Do not use the extension cord thing, your electricity will deminish and size of the cord come into play. So, do not use the cord idea.