Running electrical to a shed
Generically I'd knee-jerk to conduit and 30A 240V service with a sub-panel, but if your needs are going to be adequately met by 20A 120V power and the loading is sufficiently low that the voltage drop from 200 ft of 12Ga wire won't be a huge issue, yes, you can do that. 

Given the relative expense of digging a ditch once, and never having to dig it again if the small cost of conduit is added, I think direct burial is a terrible idea, so I'd use conduit and THWN at least for the extra 150 ft, and I'd contemplate using heavier wire than 12Ga for that 150ft to reduce voltage drop from the long run. At which point I'd be looking hard at just digging another 50 ft and doing the whole thing to a higher standard, but you may not think the way I do. 

Harper will stop in to say the 3% voltage drop rule isn't a rule (and it's not, merely a guideline), but if you get close to 20A at 200 feet on 12Ga copper you'll be down 12 volts or more - over 10% of 120V service, and generally not a good plan. But if the actual shed use will be down below 10A the 5% or so loss is unlikely to be a problem, until someone loads it up fully despite your planned use.