Ok, let's say we just started Power Grid game for 4 players: A, B, C and D. We will be focusing on Step 1st/Phase 2nd, which is the first Auction Power Plants phase in the game. We have (randomly) determined initial player order, which we can assume is now ABCD.

Exception: In the first round of the game, each player must buy a power plant.

Ok, so let's assume that this is what happens in the first round's Auction Phase:

1. A selects Power Plant, D wins the first auction.
2. B selects Power Plant, B wins the auction.
3. C selects Power Plant, C wins the auction.

Now, this would be D's turn to select the Power Plant, except he has already bought one, so he cannot bid nor offer a plant at auction.

Once a player has purchased a power plant in a round, he cannot bid in another auction in the same round, nor can he offer a plant at auction.

Does that mean we are back to A, and he selects Power Plant as the last player this round and therefore buys it at a starting price? Or was he obligated to choose plant again after D won the first auction?

Side note: I was quoting Official Rules found on RioGrandeGames.com.