Another possibility is that the old 750W PSUs that failed damaged something in both systems. Thermaltake isn't bottom of the barrel, but they aren't one of the top brands either, and depending on what PSU design they used, some can be quite awful or even dangerous in the event of a failure.
Another possibility is that you've got some electrical problems in your house... the fact that you've lost multiple monitors and power supplies in the last couple of years is a bad sign. Have you had problems with any other appliances in the house over the past few years? How old is the house and the electrical system? Though I guess its equally important to ask... all of the monitors that go into power saving mode, have you tested them hooked up to anything else like a laptop? If you can test those and they do still work... then you've probably got bad boards, PSUs, graphics cards or something else in your PCs.
Also, if you do need to replace some power supplies don't bother with such high wattages. A system that will run on a generic 700W PSU will probably work on a decent 500W (or less depending on the model) PSU from a brands like Antec, Seasonic, FSP or Corsair. The 9800GTX and 8800GT are somewhat power hungry cards, but you shouldn't need a 750W unit to run them. I ran an 8800GTX on a mid range 500W Antec PSU years ago. Also, make sure they are Active PFC... that is one of the most important features to look for in a PSU and will improve efficiency and reliability and is generally a sign of a higher quality unit.