If you are using an inverter and want to protect your PC from voltage spikes, do what you do at home -use a surge protector.
Most of the DC-DC regulators are only rated for 150 watts or so. If your PC uses more than that, you wouldn't be able to use one.
I could be wrong on this, but I think the inverter may help take care of some of regulation issue. Spikey voltage may go into the inverter but it's job is to convert that to consistent AC. Naturally, higher quality regulators would tend to have the sophistication to do this better.