You probably know Get-EventLog. This cmdlet can dump all entries from a given event log:
Get-EventLog -LogName System
However, Get-EventLog can only query one event log at a time. So if you wanted to find all errors in all event logs, you would create a loop and know the event log names.
Here is a simple trick that queries all event logs in one line:
Get-EventLog -List | Select-Object -ExpandProperty Entries -ErrorAction SilentlyContinue | Where-Object { $_.EntryType -eq 'Error' }